AP Chemistry New Course Description

8/9/2019 AP Chemistry New Course Description

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AP

CHEMISTRY

Course and Exam Description

Effective Fall 2013


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AP

CHEMISTRY

Course and Exam Description

Effective Fall 2013

The College Board

New York, NY


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About the College Board

Te College Board is a mission-driven not-or-profit organization that connects studentsto college success and opportunity. Founded in 1900, the College Board was created toexpand access to higher education. oday, the membership association is made up oover 6,000 o the worlds leading educational institutions and is dedicated to promotingexcellence and equity in education. Each year, the College Board helps more than sevenmillion students prepare or a successul transition to college through programs andservices in college readiness and college success including the SA and the AdvancedPlacement Program. Te organization also serves the education community throughresearch and advocacy on behal o students, educators and schools.

For urther inormation, visit www.collegeboard.org.

APEquity and Access Policy

Te College Board strongly encourages educators to make equitable access a guidingprinciple or their AP programs by giving all willing and academically prepared studentsthe opportunity to participate in AP. We encourage the elimination o barriers thatrestrict access to AP or students rom ethnic, racial and socioeconomic groups that havebeen traditionally underserved. Schools should make every effort to ensure their APclasses reflect the diversity o their student population. Te College Board also believesthat all students should have access to academically challenging course work beorethey enroll in AP classes, which can prepare them or AP success. It is only through acommitment to equitable preparation and access that true equity and excellence can beachieved.

AP Course and Exam Descriptions

AP course and exam descriptions are updated regularly. Please visit AP Central(apcentral.collegeboard.org) to determine whether a more recent course and examdescription PDF is available.

2013 Te College Board. College Board, Advanced Placement Program, AP, AP Central and the acorn logo are registeredtrademarks o the College Board. A ll other products and services may be trademarks o their respective owners. Visit the CollegeBoard on the Web: www.collegeboard.org.


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2013 Te College Board.

Contents

About AP........................................................................................................................ 1

About the AP Chemistry Course and Exam ...................................................................2

How AP Courses and Exams Are Developed ................................................................2

How AP Exams Are Scored .............................................................................................3

Using and Interpreting AP Scores ..................................................................................4

Additional Resources .......................................................................................................4

AP Chemistry Curriculum Framework.................................................................. 5

Changes to the Curriculum Framework .........................................................................5

Introduction ......................................................................................................................7

The Emphasis on Science Practices ........................................................................7

Overview of the Concept Outline ............................................................................8

The Concept Outline ......................................................................................................10

Big Idea 1: The chemical elements are fundamental building materials of

matter, and all matter can be understood in terms of arrangements of

atoms. These atoms retain their identity in chemical reactions......................10

Big Idea 2: Chemical and physical properties of materials can be explained

by the structure and the arrangement of atoms, ions, or molecules and

the forces between them ...............................................................................21

Big Idea 3: Changes in matter involve the rearrangement and/or reorganization

of atoms and/or the transfer of electrons .......................................................40

Big Idea 4: Rates of chemical reactions are determined by details of the

molecular collisions .......................................................................................48

Big Idea 5: The laws of thermodynamics describe the essential role of energy

and explain and predict the direction of changes in matter ............................55

Big Idea 6: Any bond or intermolecular attraction that can be formed can be

broken. These two processes are in a dynamic competition, sensitive to

initial conditions and external perturbations..................................................70

Science Practices for AP Chemistry .............................................................................84

References ......................................................................................................................89

Appendix: AP Chemistry Concepts at a Glance ..........................................................90

The Laboratory Investigations..............................................................................108

Inquiry Instruction in the AP Science Classroom .....................................................108

Time and Resources.................................................................................................. ...109

Recommended Experiments ....................................................................................... 110


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Participating in the AP Course Audit.................................................................. 112

Curricular Requirements........................................................................................... ... 112

Resource Requirements .............................................................................................. 113

Exam Information..................................................................................................... 114

How the Curriculum Framework Is Assessed......................................................... ... 117

Sample Multiple-Choice Questions ............................................................................ 118

Answers to Multiple-Choice Questions ...............................................................136

Sample Free-Response Questions .............................................................................137

Scoring Guidelines .............................................................................................143

Appendix A: Preparing Students for Success in AP Chemistry.................. 151

Appendix B: AP Chemistry Equations and Constants...................................160

Appendix C: How to Set Up a Lab Program.......................................................163


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About AP

About AP

AP enables students to pursue college-level studies while still in high school. Troughmore than 30 courses, each culminating in a rigorous exam, AP provides willing and

academically prepared students with the opportunity to earn college credit and/oradvanced placement. aking AP courses also demonstrates to college admission officersthat students have sought out the most rigorous course work available to them.

Each AP course is modeled upon a comparable college course, and college and universityaculty play a vital role in ensuring that AP courses align with college-level standards.alented and dedicated AP teachers help AP students in classrooms around the worlddevelop and apply the content knowledge and skills they will need later in college.

Each AP course concludes with a college-level assessment developed and scored bycollege and university aculty, as well as experienced AP teachers. AP Exams are an

essential part o the AP experience, enabling students to demonstrate their mastery ocollege-level course work. Most our-year colleges and universities in the United Statesand universities in 60 countries recognize AP in the admission process and grant studentscredit, placement or both on the basis o successul AP Exam scores. Visitwww.collegeboard.org/apcreditpolicy to view AP credit and placement policies at morethan 1,000 colleges and universities.

Perorming well on an AP Exam means more than just the successul completion o acourse; it is a gateway to success in college. Research consistently shows that students whoscore a 3 or higher on AP Exams typically experience greater academic success in collegeand have higher graduation rates than their non-AP peers.1Additional AP studies are

available at www.collegeboard.org/research.

1. See the ollowing research studies or more details:

Linda Hargrove, Donn Godin, and Barbara Dodd, College Outcomes Comparisons by AP and Non-AP High School Experiences(New York: Te College Board, 2008).

Chrys Dougherty, Lynn Mellor, and Shuling Jian, Te Relationship Between Advanced Placement and College Graduation (Austin, exas: National Center or Educational Accountability, 2006).

Return to the Table of Contents



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AP Chemistry Course and Exam Description

4

Using and Interpreting AP Scores

Te extensive work done by college aculty and AP teachers in the development o thecourse and the exam and throughout the scoring process ensures that AP Exam scoresaccurately represent students achievement in the equivalent college course. While

colleges and universities are responsible or setting their own credit and placementpolicies, AP scores signiy how qualified students are to receive college credit andplacement:

AP Score Qualification

5 Extremely well qualified

4 Well qualified

3 Qualified

2 Possibly qualified

1 No recommendation

Additional Resources

Visit apcentral.collegeboard.org or more inormation about the AP Program.




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AP Chemistry Curriculum Framework

AP Chemistry Curriculum

Framework

Changes to the Curriculum Framework

Since its publication in all 2011, some modifications have been made to theAP ChemistryCurriculum Framework. Te chart below summarizes the changes made, which are nowreflected in this course and exam description.

Fall 2011 Version Final Curriculum Framework

Exclusion Statements No rationale provided for exclusions. A rationale for each exclusion statement

has been provided.

Essential Knowledge 2.B.2 Dipole forces result from the attraction

among the positive ends and negative

ends of polar molecules. Hydrogenbonding is a strong type of dipole-dipole

force.

Dipole forces result from the attraction

among the positive ends and negative

ends of polar molecules. Hydrogenbonding is a strong type of dipole-dipole

force when very electronegative atoms (N,

O, and F) are involved.

Essential Knowledge

2.B.2.b

Hydrogen bonding is a relatively strong

type of intermolecular interaction that

occurs when hydrogen atoms that

are covalently bonded to the highly

electronegative atoms (N, O, and F) are

also attracted to the negative end of a

dipole formed by the electronegative atom

(N, O, and F) in a different molecule, or a

different part of the same molecule. When

hydrogen bonding is present, even smallmolecules may have strong intermolecular

attractions.

Hydrogen bonding is a relatively strong

type of intermolecular interaction

that exists when hydrogen atoms that

are covalently bonded to the highly

electronegative atoms (N, O, and F) are

also attracted to the negative end of a

dipole formed by the electronegative atom

(N, O, and F) in a different molecule or a

different part of the same molecule. When

hydrogen bonding is present, even smallmolecules may have strong intermolecular

attractions.

Table continues on following page




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6

Essential Knowledge

3.C.3.d

Many real systems do not operate

at standard conditions; the electrical

potential determination must account

for the effect of concentrations. Le

Chateliers principle can be used to predict

qualitatively the differences in electrical

potential and electron flow compared tothose at standard conditions.

Many real systems do not operate at

standard conditions and the electrical

potential determination must account

for the effect of concentrations. The

qualitative effects of concentration on

the cell potential can be understood by

considering the cell potential as a drivingforce toward equilibrium, in that the

farther the reaction is from equilibrium,

the greater the magnitude of the cell

potential. The standard cell potential, E,

corresponds to the standard conditions

of Q= 1. As the system approaches

equilibrium, the magnitude (i.e., absolute

value) of the cell potential decreases,

reaching zero at equilibrium (when Q= K).

Deviations from standard conditions that

take the cell further from equilibrium than

Q= 1 will increase the magnitude of thecell potential relative to E. Deviations

from standard conditions that take the

cell closer to equilibrium than Q= 1

will decrease the magnitude of the cell

potential relative to E. In concentration

cells, the direction of spontaneous

electron flow can be determined by

considering the direction needed to reach

equilibrium.

Essential Knowledge

3.C.3.e

The magnitude of the standard cell

potential is proportional to G (standard

Gibbs free energy) for the redox reaction

from which it is constructed.

G (standard Gibbs free energy) is

proportional to the negative of the cell

potential for the redox reaction from which

it is constructed.

Essential Knowledge 5.B.4 Calorimetry is an experimental technique

that is used to measure the change in

energy of a chemical system.

Calorimetry is an experimental technique

that is used to measure the heat

exchanged/transferred in a chemical

system.

Learning Objective 1.15 SP 6.4 added















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Introduction

Given the speed with which scientific discoveries and research continuously expandscientific knowledge, many educators are aced with the challenge o balancing breadth o

content coverage with depth o understanding. Te AP Chemistry course addresses thischallenge by ocusing on a model o instruction which promotes enduring, conceptualunderstandings and the content that supports them. Tis approach enables students tospend less time on actual recall and more time on inquiry-based learning o essentialconcepts, and helps them develop the reasoning skills necessary to engage in the sciencepractices used throughout their study o AP Chemistry.

o oster this deeper level o learning, the breadth o content coverage in AP Chemistryis defined in a way that distinguishes content essential to support the enduringunderstandings rom the many examples or applications that can overburden the course.Illustrative examples are provided that offer teachers a variety o optional instructional

contexts to help their students achieve deeper understanding. Additionally, content that isoutside the scope o the course and exam is also identified.

Students who take an AP Chemistry course, designed with this curriculum ramework asits oundation, will also develop advanced inquiry and reasoning skills, such as designinga plan or collecting data, analyzing data, applying mathematical routines, and connectingconcepts in and across domains. Te result will be readiness or the study o advancedtopics in subsequent college courses a goal o every AP course.

Te AP Chemistry course is designed to be the equivalent o the general chemistrycourse usually taken during the first college year. For some students, this course enables

them to undertake, in their first year, second-year work in the chemistry sequence attheir institution or to register in courses in other fields where general chemistry is aprerequisite. For other students, the AP Chemistry course ulfills the laboratory sciencerequirement and rees time or other courses.

The Emphasis on Science Practices

A practice is a way to coordinate knowledge and skills in order to accomplish a goal ortask. Te science practices enable students to establish lines o evidence and use them todevelop and refine testable explanations and predictions o natural phenomena. Becausecontent, inquiry, and reasoning are equally important in AP Chemistry, each learning

objective described in the concept outline combines content with inquiry and reasoningskills described in the science practices.

Te science practices that ollow the concept outline o this ramework capture importantaspects o the work that scientists engage in, at the level o competence expected o APChemistry students. AP Chemistry teachers will see within the learning objectives howthese practices are effectively integrated with the course content, and will be able to designinstruction with these practices in mind.




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Overview of the Concept Outline

Te key concepts and related content that define the revised AP Chemistry courseand exam are organized around a ew underlying principles called the big ideas, whichencompass the core scientific principles, theories, and processes governing chemical

systems. For each o the big ideas, enduring understandings, which incorporate the coreconcepts that students should retain rom the learning experience, are also identified.

Each enduring understanding is ollowed by statements o the essential knowledgenecessary to support it. Unless otherwise specified, all o the details in the outline arerequired elements o the course and may be needed to successully meet the learningobjectives tested by the AP Chemistry Exam questions. o help teachers distinguishcontent that is essential to support the enduring understandings rom the many possibleexamples and applications that can overburden a course and to see where importantconnections exist among the different content areas particular content components areemphasized as ollows:

Exclusion statementsdefine content or specific details about the content, whichdo not need to be included in the course because teaching this level o detail doesnot oster students conceptual understanding, or the level o detail representsknowledge students should have acquired prior to participating in this course.Te content in the exclusion statements will not be assessed on the AP ChemistryExam. Exclusion statements are denoted as shown in this example:

Memorization o exceptions to the Auau principle is beyond the scopeo thiscourse and the AP Exam.

Note: While excluded content will not be assessed on the AP Chemistry

Exam, such content may be provided in the body of exam questions asbackground information for the concept and science practice(s) being

assessed. The text indicates if content is excluded because it is prior

knowledge or if it is excluded because it is not essential to an understanding

of the big ideas.

Learning objectivesprovide clear and detailed articulation o what studentsshould know and be able to do. Questions or the AP Chemistry Exam will bewritten based upon both the content and the science practice designated in thelearning objectives. Each learning objective is designed to help teachers integratescience practices with specific content, and to provide them with clear inormation

about how students will be expected to demonstrate their knowledge and abilities.Alignment o the learning objectives to the science practices is denoted inbrackets. For example, in the first learning objective under 1.A.1: Te student canjustiy the observation that the ratio o the masses o the constituent elements inany pure sample o that compound is always identical on the basis o the atomicmolecular theory. [SeeSP 6.1], the bracketed reerence points to this sciencepractice: 6.1 Te student canjustiy claims with evidence.




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Note: o develop conceptual understanding, it is essential that the student candraw connections between concepts and engage in reasoning that combinesessential knowledge components rom across the curriculum ramework. Forthis reason, learning objectives may occur at the level o big ideas, enduringunderstandings, or essential knowledge. Te learning objectives are listed

immediately ollowing the description o the associated big idea, enduringunderstanding, or essential knowledge. In addition, some learning objectivesconnect to different portions o the curriculum, which is indicated with theaddition o [connects to] at the end o the learning objective.

Big Ideas

Enduring Understandings

Essential Knowledge Sciences Practices

Learning Objectives




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The Concept Outline

Big Idea 1: The chemical elements are fundamental buildingmaterials of matter, and all matter can be understood in

terms of arrangements of atoms. These atoms retain their

identity in chemical reactions.

Te atomic theory o matter is the most undamental premise o chemistry. A limitednumber o chemical elements exist, and the undamental unit o the chemical identitiesthey carry is the atom. Although atoms represent the oundational level o chemistry,observations o chemical properties are always made on collections o atoms, andmacroscopic systems involve such large numbers that they are typically counted in theunit known as the mole rather than as individual atoms. For elements, many chemicaland physical properties exhibit predictable periodicity as a unction o atomic number. In

all chemical and physical changes, atoms are conserved.

Enduring understanding 1.A: All matter is made of atoms. There

are a limited number of types of atoms; these are the elements.

Te concept o atoms as the building blocks o all matter is a undamental premise othe discipline o chemistry. Tis concept provides the oundation or conceptualizing,interpreting, and explaining the macroscopic properties and transormations observedinside and outside the laboratory in terms o the structure and properties o theconstituent materials. Te concept o the mole enables chemists to relate measured massesin the laboratory to the number o particles present in a sample. Tese two concepts also

provide the basis or the experimental determination o the purity o a sample throughchemical analysis. Te most important aspect o chemistry is not the memorization o thelaws and definitions, but rather the ability to explain how the laws and relationships arisebecause o the atomic nature o matter.

Essential knowledge 1.A.1: Molecules are composed of specificcombinations of atoms; different molecules are composed ofcombinations of different elements and of combinations of the sameelements in differing amounts and proportions.

a. Te average mass o any large number o atoms o a given element is always thesame or a given element.

b. A pure sample contains particles (or units) o one specific atom or molecule; amixture contains particles (or units) o more than one specific atom or molecule.

c. Because the molecules o a particular compound are always composed o theidentical combination o atoms in a specific ratio, the ratio o the masses o theconstituent elements in any pure sample o that compound is always the same.




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d. Pairs o elements that orm more than one type o molecule are nonethelesslimited by their atomic nature to combine in whole number ratios. Tis discretenature can be confirmed by calculating the difference in mass percent ratiosbetween such types o molecules.

Learning Objective for EK 1.A.1:

LO 1.1Te student can justiy the observation that the ratio o the masses o theconstituent elements in any pure sample o that compound is always identical onthe basis o the atomic molecular theory. [SeeSP 6.1]

Essential knowledge 1.A.2: Chemical analysis provides a method fordetermining the relative number of atoms in a substance, which can beused to identify the substance or determine its purity.

a. Because compounds are composed o atoms with known masses, there is acorrespondence between the mass percent o the elements in a compound and therelative number o atoms o each element.

b. An empirical ormula is the lowest whole number ratio o atoms in a compound.wo molecules o the same elements with identical mass percent o theirconstituent atoms will have identical empirical ormulas.

c. Because pure compounds have a specific mass percent o each element,experimental measurements o mass percents can be used to veriy the purity ocompounds.

Learning Objectives for EK 1.A.2:

LO 1.2Te student is able to select and apply mathematical routines to massdata to identiy or iner the composition o pure substances and/or mixtures.[SeeSP 2.2]

LO 1.3Te student is able to select and apply mathematical relationships to massdata in order to justiy a claim regarding the identity and/or estimated purity o asubstance. [SeeSP 2.2, 6.1]




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Essential knowledge 1.A.3: The mole is the fundamental unit forcounting numbers of particles on the macroscopic level and allowsquantitative connections to be drawn between laboratory experiments,which occur at the macroscopic level, and chemical processes, whichoccur at the atomic level.

a. Atoms and molecules interact with one another on the atomic level. Balancedchemical equations give the number o particles that react and the number oparticles produced. Because o this, expressing the amount o a substance in termso the number o particles, or moles o particles, is essential to understandingchemical processes.

b. Expressing the mass o an individual atom or molecule in atomic mass unit (amu)is useul because the average mass in amu o one particle (atom or molecule) o asubstance will always be numerically equal to the molar mass o that substance ingrams.

c. Avogadros number provides the connection between the number o moles in apure sample o a substance and the number o constituent particles (or units) othat substance.

d. Tus, or any sample o a pure substance, there is a specific numerical relationshipbetween the molar mass o the substance, the mass o the sample, and the numbero particles (or units) present.


LO 1.4Te student is able to connect the number o particles, moles, mass, andvolume o substances to one another, both qualitatively and quantitatively.[SeeSP 7.1]

Enduring understanding 1.B: The atoms of each element have

unique structures arising from interactions between electrons

and nuclei.

Te shell model arises rom experimental data. Te shell model orms a basis orunderstanding the relative energies o electrons in an atom. Te model is based on

Coulombs law and qualitatively predicts ionization energies, which can be measured inthe lab. Understanding how the shell model is consistent with the experimental data is akey learning goal or this content, beyond simple memorization o the patterns o electronconfigurations.




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Essential knowledge 1.B.1: The atom is composed of negatively chargedelectrons, which can leave the atom, and a positively charged nucleusthat is made of protons and neutrons. The attraction of the electrons tothe nucleus is the basis of the structure of the atom. Coulombs law isqualitatively useful for understanding the structure of the atom.

a. Based on Coulombs law, the orce between two charged particles is proportionalto the magnitude o each o the two charges (q1and q2), and inversely proportionalto the square o the distance, r, between them. (Potential energy is proportional toq1q2/r.) I the two charges are o opposite sign, the orce between them is attractive;i they are o the same sign, the orce is repulsive.

b. Te first ionization energy is the minimum energy needed to remove the leasttightly held electron rom an atom or ion. In general, the ionization energy o anyelectron in an atom or ion is the minimum energy needed to remove that electronrom the atom or ion.

c. Te relative magnitude o the ionization energy can be estimated throughqualitative application o Coulombs law. Te arther an electron is rom thenucleus, the lower its ionization energy. When comparing two species with thesame arrangement o electrons, the higher the nuclear charge, the higher theionization energy o an electron in a given subshell.

d. Photoelectron spectroscopy (PES) provides a useul means to engage studentsin the use o quantum mechanics to interpret spectroscopic data and extractinormation on atomic structure rom such data. In particular, low-resolutionPES o atoms provides direct evidence or the shell model. Light consists ophotons, each o which has energy E= h,where his Plancks constant and is

the requency o the light. In the photoelectric effect, incident light ejects electronsrom a material. Tis requires the photon to have sufficient energy to eject theelectron. Photoelectron spectroscopy determines the energy needed to ejectelectrons rom the material. Measurement o these energies provides a method todeduce the shell structure o an atom. Te intensity o the photoelectron signal at agiven energy is a measure o the number o electrons in that energy level.

e. Te electronic structure o atoms with multiple electrons can be inerred romevidence provided by PES. For instance, both electrons in He are identical, andthey are both roughly the same distance rom the nucleus as in H, while thereare two shells o electrons in Li, and the outermost electron is urther rom the

nucleus than in H.




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Learning Objectives for EK 1.B.1:

LO 1.5Te student is able to explain the distribution o electrons in an atom orion based upon data. [SeeSP 1.5, 6.2]

LO 1.6Te student is able to analyze data relating to electron energies orpatterns and relationships. [SeeSP 5.1]

Essential knowledge 1.B.2: The electronic structure of the atom canbe described using an electron configuration that reflects the conceptof electrons in quantized energy levels or shells; the energetics of theelectrons in the atom can be understood by consideration of Coulombslaw.

a. Electron configurations provide a method or describing the distribution o

electrons in an atom or ion.

b. Each electron in an atom has a different ionization energy, which can bequalitatively explained through Coulombs law.

c. In multielectron atoms and ions, the electrons can be thought o as being inshells and subshells, as indicated by the relatively close ionization energiesassociated with some groups o electrons. Inner electrons are called core electrons,and outer electrons are called valence electrons.

d. Core electrons are generally closer to the nucleus than valence electrons, andthey are considered to shield the valence electrons rom the ull electrostatic

attraction o the nucleus. Tis phenomenon can be used in conjunction withCoulombs law to explain/rationalize/predict relative ionization energies.Differences in electron-electron repulsion are responsible or the differences inenergy between electrons in different orbitals in the same shell.


LO 1.7Te student is able to describe the electronic structure o the atom, usingPES data, ionization energy data, and/or Coulombs law to construct explanationso how the energies o electrons within shells in atoms vary.

[SeeSP 5.1, 6.2]

LO 1.8Te student is able to explain the distribution o electrons usingCoulombs law to analyze measured energies. [SeeSP 6.2]




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Enduring understanding 1.C: Elements display periodicity in

their properties when the elements are organized according to

increasing atomic number. This periodicity can be explained

by the regular variations that occur in the electronic structures

of atoms. Periodicity is a useful principle for understandingproperties and predicting trends in properties. Its modern-day

uses range from examining the composition of materials to

generating ideas for designing new materials.

Although a simple shell model is not the currently accepted best model o atomicstructure, it is an extremely useul model that can be used qualitatively to explain and/or predict many atomic properties and trends in atomic properties. In particular, thearrangement o electrons into shells and subshells is reflected in the structure o theperiodic table and in the periodicity o many atomic properties. Many o these trends inatomic properties are important or understanding the properties o molecules, and in

being able to explain how the structure o the constituent molecules or atoms relates tothe macroscopic properties o materials. Students should be aware that the shells reflectthe quantization inherent in quantum mechanics and that the labels given to the atomicorbitals are examples o the quantum numbers used to label the resulting quantized states.Being aware o the quantum mechanical model as the currently accepted best model orthe atom is important or scientific literacy.

Essential knowledge 1.C.1: Many properties of atoms exhibit periodictrends that are reflective of the periodicity of electronic structure.

a. Te structure o the periodic table is a consequence o the pattern o electronconfigurations and the presence o shells (and subshells) o electrons in atoms.

b. Ignoring the ew exceptions, the electron configuration or an atom can bededuced rom the elements position in the periodic table.

Memorization o exceptions to the Auau principle is beyond the scopeo thiscourse and the AP Exam.

Rationale:Te mere rote recall o the exceptions does not match the goals othe curriculum revision. I given an exception on the AP Exam, students will beresponsible or providing possible reasons or the exceptions based on theory.

c. For many atomic properties, trends within the periodic table (and relative valuesor different atoms and ions) can be qualitatively understood and explained usingCoulombs law, the shell model, and the concept o shielding/effective nuclearcharge. Tese properties include:

1. First ionization energy

2. Atomic and ionic radii




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3. Electronegativity

4. ypical ionic charges

d. Periodicity is a useul tool when designing new molecules or materials, sincereplacing an element o one group with another o the same group may lead to a

new substance with similar properties. For instance, since SiO2can be a ceramic,SnO2may be as well.

Learning Objectives for EK 1.C.1:

LO 1.9Te student is able to predict and/or justiy trends in atomic propertiesbased on location on the periodic table and/or the shell model. [SeeSP 6.4]

LO 1.10Students can justiy with evidence the arrangement o the periodic tableand can apply periodic properties to chemical reactivity.[SeeSP 6.1]

LO 1.11Te student can analyze data, based on periodicity and the propertieso binary compounds, to identiy patterns and generate hypotheses related to themolecular design o compounds or which data are not supplied. [SeeSP 3.1, 5.1]

Essential knowledge 1.C.2: The currently accepted best model of theatom is based on the quantum mechanical model.

a. Coulombs law is the basis or describing the energy o interaction betweenprotons and electrons.

b. Electrons are not considered to ollow specific orbits. Chemists reer to the regiono space in which an electron is ound as an orbital.

c. Electrons in atoms have an intrinsic property known as spin that can result inatoms having a magnetic moment. Tere can be at most two electrons in anyorbital, and these electrons must have opposite spin.

d. Te quantum mechanical (QM) model addresses known problems with theclassical shell model and is also consistent with atomic electronic structures thatcorrespond with the periodic table.

e. Te QM model can be approximately solved using computers and serves as the

basis or sofware that calculates the structure and reactivity o molecules.

Assignment o quantum numbers to electrons is beyond the scopeo this course andthe AP Exam.

Rationale:Assignment o quantum numbers to electrons does not increase studentsconceptual understanding o quantum theory.




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Learning Objective for EK 1.C.2:

LO 1.12Te student is able to explain why a given set o data suggests, or doesnot suggest, the need to refine the atomic model rom a classical shell model withthe quantum mechanical model. [SeeSP 6.3]

Enduring understanding 1.D: Atoms are so small that they are

difficult to study directly; atomic models are constructed to

explain experimental data on collections of atoms.

Because the experimental measurement o ionization energy provides a window into theoverall electronic structure o the atom, this content provides rich opportunities to explorehow scientific models can be constructed and refined in response to available data. Temodern use o mass spectrometry provides another example o how experimental datacan be used to test or reject a scientific model.

Essential knowledge 1.D.1: As is the case with all scientific models, anymodel of the atom is subject to refinement and change in response tonew experimental results. In that sense, an atomic model is not regardedas an exact description of the atom, but rather a theoretical constructthat fits a set of experimental data.

a. Scientists use experimental results to test scientific models. When experimentalresults are not consistent with the predictions o a scientific model, the model mustbe revised or replaced with a new model that is able to predict/explain the new

experimental results. A robust scientific model is one that can be used to explain/predict numerous results over a wide range o experimental circumstances.

b. Te construction o a shell model o the atom through ionization energyinormation provides an opportunity to show how a model can be refined andchanged as additional inormation is considered.

Learning Objective for EK 1.D.1:

LO 1.13Given inormation about a particular model o the atom, the student isable to determine i the model is consistent with specified evidence. [SeeSP 5.3]




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Essential knowledge 1.D.2: An early model of the atom stated that allatoms of an element are identical. Mass spectrometry data demonstrateevidence that contradicts this early model.

a. Data rom mass spectrometry demonstrate evidence that an early model o the

atom (Daltons model) is incorrect; these data then require a modification o thatmodel.

b. Data rom mass spectrometry also demonstrate direct evidence o differentisotopes rom the same element.

c. Te average atomic mass can be estimated rom mass spectra.

Learning Objective for EK 1.D.2:

LO 1.14Te student is able to use data rom mass spectrometry to identiy the

elements and the masses o individual atoms o a specific element.[SeeSP 1.4, 1.5]

Essential knowledge 1.D.3: The interaction of electromagnetic waves orlight with matter is a powerful means to probe the structure of atomsand molecules, and to measure their concentration.

a. Te energy o a photon is related to the requency o the electromagnetic wavethrough Plancks equation (E= h). When a photon is absorbed (or emitted) bya molecule, the energy o the molecule is increased (or decreased) by an amount

equal to the energy o the photon.b. Different types o molecular motion lead to absorption or emission o photons

in different spectral regions. Inrared radiation is associated with transitions inmolecular vibrations and so can be used to detect the presence o different typeso bonds. Ultraviolet/visible radiation is associated with transitions in electronicenergy levels and so can be used to probe electronic structure.

c. Te amount o light absorbed by a solution can be used to determine theconcentration o the absorbing molecules in that solution, via the Beer-Lambertlaw.




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Learning Objectives for EK 1.D.3:

LO 1.15Te student can justiy the selection o a particular type o spectroscopyto measure properties associated with vibrational or electronic motions omolecules. [SeeSP 4.1, 6.4]

LO 1.16Te student can design and/or interpret the results o an experimentregarding the absorption o light to determine the concentration o an absorbingspecies in a solution. [SeeSP 4.2, 5.1]

Enduring understanding 1.E: Atoms are conserved in physical

and chemical processes.

Te conservation o mass in chemical and physical transormations is a undamentalconcept, and is a reflection o the atomic model o matter. Tis concept plays a key role in

much o chemistry, in both quantitative determinations o quantities o materials involvedin chemical systems and transormations, and in the conceptualization and representationo those systems and transormations.

Essential knowledge 1.E.1: Physical and chemical processes can bedepicted symbolically; when this is done, the illustration must conserveall atoms of all types.

a. Various types o representations can be used to show that matter is conservedduring chemical and physical processes.

1. Symbolic representations2. Particulate drawings

b. Because atoms must be conserved during a chemical process, it is possible tocalculate product masses given known reactant masses, or to calculate reactantmasses given product masses.

c. Te concept o conservation o atoms plays an important role in the interpretationand analysis o many chemical processes on the macroscopic scale. Conservationo atoms should be related to how nonradioactive atoms are neither lost nor gainedas they cycle among land, water, atmosphere, and living organisms.

Learning Objective for EK 1.E.1:

LO 1.17Te student is able to express the law o conservation o massquantitatively and qualitatively using symbolic representations and particulatedrawings. [SeeSP 1.5]




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Essential knowledge 1.E.2: Conservation of atoms makes it possibleto compute the masses of substances involved in physical andchemical processes. Chemical processes result in the formation of newsubstances, and the amount of these depends on the number and thetypes and masses of elements in the reactants, as well as the efficiency

of the transformation.

a. Te number o atoms, molecules, or ormula units in a given mass o substancecan be calculated.

b. Te subscripts in a chemical ormula represent the number o atoms o each typein a molecule.

c. Te coefficients in a balanced chemical equation represent the relative numbers oparticles that are consumed and created when the process occurs.

d. Te concept o conservation o atoms plays an important role in the interpretation

and analysis o many chemical processes on the macroscopic scale.e. In gravimetric analysis, a substance is added to a solution that reacts specifically

with a dissolved analyte (the chemical species that is the target o the analysis) toorm a solid. Te mass o solid ormed can be used to iner the concentration othe analyte in the initial sample.

. itrations may be used to determine the concentration o an analyte in a solution.Te titrant has a known concentration o a species that reacts specificallywith the analyte. Te equivalence o the titration occurs when the analyte istotally consumed by the reacting species in the titrant. Te equivalence point isofen indicated by a change in a property (such as color) that occurs when the

equivalence point is reached. Tis observable event is called the end point o thetitration.

Learning Objectives for EK 1.E.2:

LO 1.18Te student is able to apply conservation o atoms to the rearrangemento atoms in various processes. [SeeSP 1.4]

LO 1.19Te student can design, and/or interpret data rom, an experimentthat uses gravimetric analysis to determine the concentration o an analyte in a

solution. [SeeSP 4.2, 5.1, 6.4]LO 1.20Te student can design, and/or interpret data rom, an experiment thatuses titration to determine the concentration o an analyte in a solution.[SeeSP 4.2, 5.1, 6.4]




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Solutions are an important class o mixtures; o particular importance is a conceptualunderstanding on the molecular level o the structure and composition o a liquidsolution. In addition, the energetics o solution ormation can be understood qualitativelythrough consideration o the interactions and structure o the components beore andafer the creation o the solution.

Essential knowledge 2.A.1: The different properties of solids andliquids can be explained by differences in their structures, both at theparticulate level and in their supramolecular structures.

a. Solids can be crystalline, where the particles are arranged in a regular 3-Dstructure, or they can be amorphous, where the particles do not have a regular,orderly arrangement. In both cases, the motion o the individual particles islimited, and the particles do not undergo any overall translation with respect toeach other. Interparticle interactions and the ability to pack the particles togetherprovide the main criteria or the structures o solids.

b. Te constituent particles in liquids are very close to each other, and they arecontinually moving and colliding. Te particles are able to undergo translationwith respect to each other and their arrangement, and movement is influenced bythe nature and strength o the intermolecular orces that are present.

c. Te solid and liquid phases or a particular substance generally have relativelysmall differences in molar volume because in both cases the constituent particlesare very close to each other at all times.

d. Te differences in other properties, such as viscosity, surace tension, and volumeso mixing (or liquids), and hardness and macroscopic crystal structure (or

solids), can be explained by differences in the strength o attraction between theparticles and/or their overall organization.

e. Heating and cooling curves or pure substances provide insight into the energeticso liquid/solid phase changes.


LO 2.3Te student is able to use aspects o particulate models (i.e., particlespacing, motion, and orces o attraction) to reason about observed differences

between solid and liquid phases and among solid and liquid materials.[SeeSP 6.4, 7.1]




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Essential knowledge 2.A.2: The gaseous state can be effectivelymodeled with a mathematical equation relating various macroscopicproperties. A gas has neither a definite volume nor a definite shape;because the effects of attractive forces are minimal, we usually assumethat the particles move independently.

a. Ideal gases exhibit specific mathematical relationships among the number oparticles present, the temperature, the pressure, and the volume.

b. In a mixture o ideal gases, the pressure exerted by each component (the partialpressure) is independent o the other components. Tereore, the total pressure isthe sum o the partial pressures.

c. Graphical representations o the relationships between P, V, and are useul todescribe gas behavior.

d. Kinetic molecular theory combined with a qualitative use o the Maxwell-

Boltzmann distribution provides a robust model or qualitative explanations othese mathematical relationships.

e. Some real gases exhibit ideal or near-ideal behavior under typical laboratoryconditions. Laboratory data can be used to generate or investigate the relationshipsin 2.A.2.a and to estimate absolute zero on the Celsius scale.

. All real gases are observed to deviate rom ideal behavior, particularly underconditions that are close to those resulting in condensation. Except at extremelyhigh pressures that are not typically seen in the laboratory, deviations romideal behavior are the result o intermolecular attractions among gas molecules.Tese orces are strongly distance-dependent, so they are most significant during

collisions.

g. Observed deviations rom ideal gas behavior can be explained through anunderstanding o the structure o atoms and molecules and their intermolecularinteractions.

Phase diagrams are beyond the scopeo this course and the AP Exam.

Rationale:Phase diagrams are standard in all high school chemistry textbooks andthereore are considered prior knowledge.




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LO 2.4Te student is able to use KM and concepts o intermolecular orces tomake predictions about the macroscopic properties o gases, including both idealand nonideal behaviors. [SeeSP 1.4, 6.4]

LO 2.5Te student is able to refine multiple representations o a sample o matterin the gas phase to accurately represent the effect o changes in macroscopicproperties on the sample. [SeeSP 1.3, 6.4, 7.2]

LO 2.6Te student can apply mathematical relationships or estimation todetermine macroscopic variables or ideal gases. [SeeSP 2.2, 2.3]

Essential knowledge 2.A.3: Solutions are homogenous mixtures in whichthe physical properties are dependent on the concentration of the solute

and the strengths of all interactions among the particles of the solutesand solvent.

a. In a solution (homogeneous mixture), the macroscopic properties do not varythroughout the sample. Tis is in contrast to a heterogeneous mixture in whichthe macroscopic properties depend upon the location in the mixture. Tedistinction between heterogeneous and homogeneous depends on the lengthscale o interest. As an example, colloids may be heterogeneous on the scale omicrometers, but homogeneous on the scale o centimeters.

b. Solutions come in the orm o solids, liquids, and gases.

c. For liquid solutions, the solute may be a gas, a liquid, or a solid.

d. Based on the reflections o their structure on the microscopic scale, liquidsolutions exhibit several general properties:

1. Te components cannot be separated by using filter paper.

2. Tere are no components large enough to scatter visible light.

3. Te components can be separated using processes that are a result o theintermolecular interactions between and among the components.

e. Chromatography (paper and column) separates chemical species by takingadvantage o the differential strength o intermolecular interactions between andamong the components.

. Distillation is used to separate chemical species by taking advantage o thedifferential strength o intermolecular interactions between and among thecomponents and the effects these interactions have on the vapor pressures o thecomponents in the mixture.




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g. Te ormation o a solution may be an exothermic or endothermic process,depending on the relative strengths o intermolecular/interparticle interactionsbeore and afer the dissolution process.

h. Generally, when ionic compounds are dissolved in water, the component ions are

separated and dispersed. Te presence o ions in a solution can be detected by useo conductivity measurements.

i. Solution composition can be expressed in a variety o ways; molarity is the mostcommon method used in the laboratory. Molarity is defined as the number omoles o solute per liter o solution.

j. Understanding how to prepare solutions o specified molarity through directmixing o the components, through use o volumetric glassware, and bydilution o a solution o known molarity with additional solvent is important orperorming laboratory work in chemistry.

Colligative properties are beyond the scopeo this course and the AP Exam and arethereore considered prior knowledge and not directly assessed on the exam.

Calculations o molality, percent by mass, and percent by volume are beyond thescopeo this course and the AP Exam.

Rationale:Molality pertains to colligative properties, which are considered priorknowledge and thereore molality will not be assessed on the exam.


LO 2.7Te student is able to explain how solutes can be separated by

chromatography based on intermolecular interactions. [SeeSP 6.2]

LO 2.8Te student can draw and/or interpret representations o solutions thatshow the interactions between the solute and solvent. [SeeSP 1.1, 1.2, 6.4]

LO 2.9Te student is able to create or interpret representations that link theconcept o molarity with particle views o solutions. [SeeSP 1.1, 1.4]

LO 2.10Te student can design and/or interpret the results o a separationexperiment (filtration, paper chromatography, column chromatography, ordistillation) in terms o the relative strength o interactions among and betweenthe components. [SeeSP 4.2, 5.1, 6.4]




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Enduring understanding 2.B: Forces of attraction between

particles (including the noble gases and also different parts

of some large molecules) are important in determining many

macroscopic properties of a substance, including how the

observable physical state changes with temperature.Chemists categorize intermolecular interactions based on the structural eatures givingrise to the interaction. Although there are some trends in the relative strengths othese interactions, the specific structure and size o the particles involved can play avery important role in determining the overall strength o a particular intermolecular(or intramolecular) interaction. Te properties o condensed phases and o manycrucial biological structures are determined by the nature and strength o theseinteractions. Deviation rom ideal gas behavior is generally a reflection o the presenceo intermolecular interactions between gas particles. Tus, in all phases, the structure oparticles on the molecular level is directly related to the properties o both the particles

themselves and the behavior o macroscopic collections o those molecules.

Essential knowledge 2.B.1: London dispersion forces are attractive forcespresent between all atoms and molecules. London dispersion forces areoften the strongest net intermolecular force between large molecules.

a. A temporary, instantaneous dipole may be created by an uneven distribution oelectrons around the nucleus (nuclei) o an atom (molecule).

b. London dispersion orces arise due to the Coulombic interaction o the temporarydipole with the electron distribution in neighboring atoms and molecules.

c. Dispersion orces increase with contact area between molecules and withincreasing polarizability o the molecules. Te polarizability o a moleculeincreases with the number o electrons in the molecule, and is enhanced by thepresence o pi bonding.

Learning Objective for EK 2.B.1:

LO 2.11Te student is able to explain the trends in properties and/or predictproperties o samples consisting o particles with no permanent dipole on thebasis o London dispersion orces. [SeeSP 6.2, 6.4]




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Essential knowledge 2.B.2: Dipole forces result from the attraction amongthe positive ends and negative ends of polar molecules. Hydrogenbonding is a strong type of dipole-dipole force that exists when veryelectronegative atoms (N, O, and F) are involved.

a. Molecules with dipole moments experience Coulombic interactions that result in anet attractive interaction when they are near each other.

1. Intermolecular dipole-dipole orces are weaker than ionic orces or covalentbonds.

2. Interactions between polar molecules are typically greater than betweennonpolar molecules o comparable size because these interactions act inaddition to London dispersion orces.

3. Dipole-dipole attractions can be represented by diagrams o attractionbetween the positive and negative ends o polar molecules trying to maximize

attractions and minimize repulsions in the liquid or solid state.4. Dipole-induced dipole interactions are present between a polar and nonpolar

molecule. Te strength o these orces increases with the magnitude o thedipole o the polar molecule and with the polarizability o the nonpolarmolecule.

b. Hydrogen bonding is a relatively strong type o intermolecular interactionthat exists when hydrogen atoms that are covalently bonded to the highlyelectronegative atoms (N, O, and F) are also attracted to the negative end o adipole ormed by the electronegative atom (N, O, and F) in a different molecule,or a different part o the same molecule. When hydrogen bonding is present, even

small molecules may have strong intermolecular attractions.

Other cases o much weaker hydrogen bonding are beyond the scopeo theAP Chemistry course and exam.

Rationale:Te hydrogen bonding that occurs when hydrogen is bonded to highlyelectronegative atoms (N, O, and F) will be emphasized as will the electrostaticversus covalent nature o the bond. We will not include other cases o much weakerhydrogen bonding in the AP Chemistry course.

c. Hydrogen bonding between molecules, or between different parts o a singlemolecule, may be represented by diagrams o molecules with hydrogen bonding

and indications o location o hydrogen bonding.d. Ionic interactions with dipoles are important in the solubility o ionic compounds

in polar solvents.




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LO 2.12Te student can qualitatively analyze data regarding real gasesto identiy deviations rom ideal behavior and relate these to molecularinteractions.[SeeSP 5.1, 6.5, connects to2.A.2]

LO 2.13Te student is able to describe the relationships between the structuraleatures o polar molecules and the orces o attraction between the particles.[SeeSP 1.4, 6.4]

LO 2.14Te student is able to apply Coulombs law qualitatively (including usingrepresentations) to describe the interactions o ions, and the attractions betweenions and solvents to explain the actors that contribute to the solubility o ioniccompounds. [SeeSP 1.4, 6.4]

Essential knowledge 2.B.3: Intermolecular forces play a key role indetermining the properties of substances, including biological structuresand interactions.

a. Many properties o liquids and solids are determined by the strengths and types ointermolecular orces present.

1. Boiling point

2. Surace tension

3. Capillary action

4. Vapor pressure

b. Substances with similar intermolecular interactions tend to be miscible or solublein one another.

c. Te presence o intermolecular orces among gaseous particles, including noblegases, leads to deviations rom ideal behavior, and it can lead to condensation atsufficiently low temperatures and/or sufficiently high pressures.

d. Graphs o the pressure-volume relationship or real gases can demonstrate thedeviation rom ideal behavior; these deviations can be interpreted in terms o thepresence and strengths o intermolecular orces.




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e. Te structure and unction o many biological systems depend on the strength andnature o the various Coulombic orces.

1. Substrate interactions with the active sites in enzyme catalysis

2. Hydrophilic and hydrophobic regions in proteins that determine three-

dimensional structure in water solutions


LO 2.15Te student is able to explain observations regarding the solubility oionic solids and molecules in water and other solvents on the basis o particleviews that include intermolecular interactions and entropic effects. [SeeSP 1.4,6.2, connects to5.E.1]

LO 2.16Te student is able to explain the properties (phase, vapor pressure,

viscosity, etc.) o small and large molecular compounds in terms o the strengthsand types o intermolecular orces. [SeeSP 6.2]

Enduring understanding 2.C: The strong electrostatic forces of

attraction holding atoms together in a unit are called chemical

bonds.

Covalent bonds, ionic bonds, and metallic bonds are distinct rom (and significantlystronger than) typical intermolecular interactions. Electronegativity can be used to reasonabout the type o bonding present between two atoms. Covalent chemical bonds can be

modeled as the sharing o one or more pairs o valence electrons between two atoms in amolecule. Te extent to which this sharing is unequal can be predicted rom the relativeelectronegativities o the atoms involved; the relative electronegativities can generallybe understood through application o the shell model and Coulombs law. Te Lewisstructure model, combined with valence shell electron pair repulsion (VSEPR), can beused to predict many structural eatures o covalently bonded molecules and ions. Ionicbonding is the phrase used to describe the strong Coulombic interaction between ions inan ionic substance. Te bonding in metals is characterized by delocalization o valenceelectrons.

Learning Objective for EU 2.C:

LO 2.17Te student can predict the type o bonding present between twoatoms in a binary compound based on position in the periodic table and theelectronegativity o the elements. [SeeSP 6.4]




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Essential knowledge 2.C.1: In covalent bonding, electrons are sharedbetween the nuclei of two atoms to form a molecule or polyatomic ion.Electronegativity differences between the two atoms account for thedistribution of the shared electrons and the polarity of the bond.

a. Electronegativity is the ability o an atom in a molecule to attract shared electronsto it.

b. Electronegativity values or the representative elements increase going rom lefto right across a period and decrease going down a group. Tese trends can beunderstood qualitatively through the electronic structure o the atoms, the shellmodel, and Coulombs law.

c. wo or more valence electrons shared between atoms o identical electronegativityconstitute a nonpolar covalent bond.

d. However, bonds between carbon and hydrogen are ofen considered to be

nonpolar even though carbon is slightly more electronegative than hydrogen. Teormation o a nonpolar covalent bond can be represented graphically as a plot opotential energy vs. distance or the interaction o two identical atoms. Hydrogenatoms are ofen used as an example.

1. Te relative strengths o attractive and repulsive orces as a unction odistance determine the shape o the graph.

2. Te bond length is the distance between the bonded atoms nuclei, and is thedistance o minimum potential energy where the attractive and repulsiveorces are balanced.

3. Te bond energy is the energy required or the dissociation o the bond. Tisis the net energy o stabilization o the bond compared to the two separatedatoms. ypically, bond energy is given on a per mole basis.

e. wo or more valence electrons shared between atoms o unequal electronegativityconstitute a polar covalent bond.

1. Te difference in electronegativity or the two atoms involved in a polarcovalent bond is not equal to zero.

2. Te atom with a higher electronegativity will develop a partial negative chargerelative to the other atom in the bond. For diatomic molecules, the partial

negative charge on the more electronegative atom is equal in magnitude to thepartial positive charge on the less electronegative atom.

3. Greater differences in electronegativity lead to greater partial charges, andconsequently greater bond dipoles.

4. Te sum o partial charges in any molecule or ion must be equal to the overallcharge on the species.




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. All bonds have some ionic character, and the difference between ionic andcovalent bonding is not distinct but rather a continuum. Te difference inelectronegativity is not the only actor in determining i a bond is designatedionic or covalent. Generally, bonds between a metal and nonmetal are ionic, andbetween two nonmetals the bonds are covalent. Examination o the properties o

a compound is the best way to determine the type o bonding.


LO 2.18Te student is able to rank and justiy the ranking o bond polarity onthe basis o the locations o the bonded atoms in the periodic table. [SeeSP 6.1]

Essential knowledge 2.C.2: Ionic bonding results from the net attractionbetween oppositely charged ions, closely packed together in a crystal

lattice.

a. Te cations and anions in an ionic crystal are arranged in a systematic, periodic3-D array that maximizes the attractive orces among cations and anions whileminimizing the repulsive orces.

Knowledge o specific types o crystal structures is beyond the scopeo this courseand the AP Exam.

Rationale:Te study o crystal structures does not strengthen understanding o thebig ideas.

b. Coulombs law describes the orce o attraction between the cations and anions in

an ionic crystal.

1. Because the orce is proportional to the charge on each ion, larger charges leadto stronger interactions.

2. Because the orce is inversely proportional to the square o the distancebetween the centers o the ions (nuclei), smaller ions lead to strongerinteractions.


LO 2.19Te student can create visual representations o ionic substancesthat connect the microscopic structure to macroscopic properties, and/or userepresentations to connect the microscopic structure to macroscopic properties(e.g., boiling point, solubility, hardness, brittleness, low volatility, lack omalleability, ductility, or conductivity). [SeeSP 1.1, 1.4, 7.1, connects to2.D.1,2.D.2]




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Essential knowledge 2.C.3: Metallic bonding describes an array ofpositively charged metal cores surrounded by a sea of mobile valenceelectrons.

a. Te valence electrons rom the metal atoms are considered to be delocalized and

not associated with any individual atom.b. Metallic bonding can be represented as an array o positive metal ions with

valence electrons drawn among them, as i the electrons were moving (i.e., a sea oelectrons).

c. Te electron sea model can be used to explain several properties o metals,including electrical conductivity, malleability, ductility, and low volatility.

d. Te number o valence electrons involved in metallic bonding, via the shell model,can be used to understand patterns in these properties, and can be related to theshell model to reinorce the connections between metallic bonding and other

orms o bonding.


LO 2.20Te student is able to explain how a bonding model involvingdelocalized electrons is consistent with macroscopic properties o metals (e.g.,conductivity, malleability, ductility, and low volatility) and the shell model o theatom. [SeeSP 6.2, 7.1, connects to2.D.2]

Essential knowledge 2.C.4: The localized electron bonding modeldescribes and predicts molecular geometry using Lewis diagrams andthe VSEPR model.

a. Lewis diagrams can be constructed according to a well-established set oprinciples.

b. Te VSEPR model uses the Coulombic repulsion between electrons as a basis orpredicting the arrangement o electron pairs around a central atom.

c. In cases where more than one equivalent Lewis structure can be constructed,resonance must be included as a refinement to the Lewis structure approach in

order to provide qualitatively accurate predictions o molecular structure andproperties (in some cases).

d. Formal charge can be used as a criterion or determining which o several possiblevalid Lewis diagrams provides the best model or predicting molecular structureand properties.

Te use o ormal charge to explain why certain molecules do not obey the octet ruleis beyond the scopeo this course and the AP Exam.




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Rationale:Explaining why certain molecules do NO obey the octet rule is beyondthe scopeo the course. Te scope o the course DOES include the use o ormalcharge to evaluate different structures that ollow the octet rule and the limitationso using Lewis structures or molecules with odd numbers o electrons or expandedoctets.

e. Te combination o Lewis diagrams with the VSEPR model provides a powerulmodel or predicting structural properties o many covalently bonded moleculesand polyatomic ions, including the ollowing:

1. Molecular geometry

2. Bond angles

3. Relative bond energies based on bond order

4. Relative bond lengths (multiple bonds, effects o atomic radius)

5. Presence o a dipole moment. As with any model, there are limitations to the use o the Lewis structure model,

particularly in cases with an odd number o valence electrons. Recognizing thatLewis diagrams have limitations is o significance.

Learning how to deend Lewis models based on assumptions about the limitations othe models is beyond the scopeo this course and the AP Exam.

Rationale:Learning how to deend Lewis models does not strengthen understandingo the big ideas.

g. Organic chemists commonly use the terms hybridization and hybrid orbital

to describe the arrangement o electrons around a central atom. When there isa bond angle o 180, the central atom is said to be sp hybridized; or 120, thecentral atom is sp2hybridized; and or 109, the central atom is sp3hybridized.Students should be aware o this terminology, and be able to use it. When an atomhas more than our pairs o electrons surrounding the central atom, students areonly responsible or the shape o the resulting molecule.

An understanding o the derivation and depiction o these orbitals is beyond thescopeo this course and the AP Exam. Current evidence suggests that hybridizationinvolving d orbitals does not exist, and there is controversy about the need to teachany hybridization. Until there is agreement in the chemistry community, we will

continue to include sp, sp2

, and sp3

hybridization in the current course.Rationale:Te course includes the distinction between sigma and pi bonding,the use o VSEPR to explain the shapes o molecules, and the sp, sp 2, and sp3nomenclature. Additional aspects related to hybridization are both controversialand do not substantially enhance understanding o molecular structure.

h. Bond ormation is associated with overlap between atomic orbitals. In multiplebonds, such overlap leads to the ormation o both sigma and pi bonds. Te overlap




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is stronger in sigma than pi bonds, which is reflected in sigma bonds having largerbond energy than pi bonds. Te presence o a pi bond also prevents the rotation othe bond, and leads to structural isomers. In systems, such as benzene, where atomicp-orbitals overlap strongly with more than one other p-orbital, extended pi bondingexists, which is delocalized across more than two nuclei. Such descriptions provide

an alternative description to resonance in Lewis structures. A useul example odelocalized pi bonding is molecular solids that conduct electricity. Te discoveryo such materials at the end o the 1970s overturned a long-standing assumption inchemistry that molecular solids will always be insulators.

i. Molecular orbital theory describes covalent bonding in a manner that cancapture a wider array o systems and phenomena than the Lewis or VSEPRmodels. Molecular orbital diagrams, showing the correlation between atomic andmolecular orbitals, are a useul qualitative tool related to molecular orbital theory.

Other aspects o molecular orbital theory, such as recall or filling o molecularorbital diagrams, are beyond the scopeo this course and the AP Exam.

Rationale:As currently covered in reshman college chemistry textbooks, molecularorbital theory is superficially taught and limited to homonuclear molecules in thesecond period. Algorithmic filling o such MO diagrams does not lead to a deeperconceptual understanding o bonding. Te course does include the importantdistinction between sigma and pi bonding.


LO 2.21Te student is able to use Lewis diagrams and VSEPR to predict the

geometry o molecules, identiy hybridization, and make predictions aboutpolarity. [SeeSP 1.4]

Enduring understanding 2.D: The type of bonding in the solid

state can be deduced from the properties of the solid state.

In solids, the properties o the material reflect the nature and strength o the interactionsbetween the constituent particles. For this reason, the type o bonding that predominatesin a solid material, and the nature o the interactions between the particles comprising thesolid, can generally be inerred rom the observed macroscopic properties o the material.Properties such as vapor pressure, conductivity as a solid and in aqueous solution, andrelative brittleness or hardness can generally be explained in this way.

Although recognizing the properties that can be associated with a particular type obonding is valuable in categorizing materials, relating those properties to the structureo the materials on the molecular scale, and being able to make reasoned predictions othe properties o a solid based on its constituent particles, provides evidence o deeperconceptual understanding.




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Learning Objective for EU 2.D:

LO 2.22Te student is able to design or evaluate a plan to collect and/orinterpret data needed to deduce the type o bonding in a sample o a solid. [SeeSP 4.2, 6.4]

Essential knowledge 2.D.1: Ionic solids have high melting points, arebrittle, and conduct electricity only when molten or in solution.

a. Many properties o ionic solids are related to their structure.

1. Ionic solids generally have low vapor pressure due to the strong Coulombicinteractions o positive and negative ions arranged in a regular three-dimensional array.

2. Ionic solids tend to be brittle due to the repulsion o like charges caused whenone layer slides across another layer.

3. Ionic solids do not conduct electricity. However, when ionic solids are melted,they do conduct electricity because the ions are ree to move.

4. When ionic solids are dissolved in water, the separated ions are ree to move;thereore, these solutions will conduct electricity. Dissolving a nonconductingsolid in water, and observing the solutions ability to conduct electricity, is oneway to identiy an ionic solid.

5. Ionic compounds tend not to dissolve in nonpolar solvents because the

attractions among the ions are much stronger than the attractions among theseparated ions and the nonpolar solvent molecules.

b. Te attractive orce between any two ions is governed by Coulombs law: Te orceis directly proportional to the charge o each ion and inversely proportional to thesquare o the distance between the centers o the ions.

1. For ions o a given charge, the smaller the ions, and thus the smaller thedistance between ion centers, the stronger the Coulombic orce o attraction,and the higher the melting point.

2. Ions with higher charges lead to higher Coulombic orces, and thereore higher

melting points. Te study o the specific varieties o crystal lattices or ionic compounds is beyond

the scopeo this course and the AP Exam.

Rationale:Tis topic has not been part o AP Chemistry or many years andincluding the topic in the new course was not viewed as the best way to deepenunderstanding o the big ideas.




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LO 2.23Te student can create a representation o an ionic solid that showsessential characteristics o the structure and interactions present in thesubstance. [SeeSP 1.1]

LO 2.24Te student is able to explain a representation that connects propertieso an ionic solid to its structural attributes and to the interactions present at theatomic level. [SeeSP 1.1, 6.2, 7.1]

Essential knowledge 2.D.2: Metallic solids are good conductors of heatand electricity, have a wide range of melting points, and are shiny,malleable, ductile, and readily alloyed.

a. A metallic solid can be represented as positive kernels (or cores) consisting o the

nucleus and inner electrons o each atom surrounded by a sea o mobile valenceelectrons.

1. Metals are good conductors because the electrons are delocalized and relativelyree to move.

2. Metals are malleable and ductile because deorming the solid does not changethe environment immediately surrounding each metal core.

b. Metallic solids are ofen pure substances, but may also be mixtures called alloys.

1. Some properties o alloys can be understood in terms o the size o the

component atoms: Interstitial alloys orm between atoms o different radius, where the smalleratoms fill the interstitial spaces between the larger atoms. (Steel is an examplein which carbon occupies the interstices in iron.) Te interstitial atoms makethe lattice more rigid, decreasing malleability and ductility. Substitutional alloys orm between atoms o comparable radius, where oneatom substitutes or the other in the lattice. (Brass is an example in whichsome copper atoms are substituted with a different element, usually zinc.) Tedensity typically lies between those o the component metals, and the alloyremains malleable and ductile.

2. Alloys typically retain a sea o mobile electrons and so remain conducting.3. In some cases, alloy ormation alters the chemistry o the surace. An example

is ormation o a chemically inert oxide layer in stainless steel.




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LO 2.25Te student is able to compare the properties o metal alloys with theirconstituent elements to determine i an alloy has ormed, identiy the type oalloy ormed, and explain the differences in properties using particulate levelreasoning. [SeeSP 1.4, 7.2]

LO 2.26Students can use the electron sea model o metallic bonding to predictor make claims about the macroscopic properties o metals or alloys.[SeeSP 6.4, 7.1]

LO 2.27Te student can create a representation o a metallic solid that showsessential characteristics o the structure and interactions present in the substance.[SeeSP 1.1]

LO 2.28Te student is able to explain a representation that connects properties

o a metallic solid to its structural attributes and to the interactions present at theatomic level. [SeeSP 1.1, 6.2, 7.1]

Essential knowledge 2.D.3: Covalent network solids generally haveextremely high melting points, are hard, and are thermal insulators.Some conduct electricity.

a. Covalent network solids consist o atoms that are covalently bonded together intoa two-dimensional or three-dimensional network.

1. Covalent network solids are only ormed rom nonmetals: elemental (diamond,graphite) or two nonmetals (silicon dioxide and silicon carbide).

2. Te properties o covalent network solids are a reflection o their structure.

3. Covalent network solids have high melting points because all o the atoms arecovalently bonded.

4. Tree-dimensional covalent networks tend to be rigid and hard because thecovalent bond angles are fixed.

5. Generally, covalent network solids orm in the carbon group because o theirability to orm our covalent bonds.

b. Graphite is an allotrope o carbon that orms sheets o two-dimensional networks.

1. Graphite has a high melting point because the covalent bonds between thecarbon atoms making up each layer are relatively strong.

2. Graphite is sof because adjacent layers can slide past each other relatively easily;the major orces o attraction between the layers are London dispersion orces.




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c. Silicon is a covalent network solid and a semiconductor.

1. Silicon orms a three-dimensional network similar in geometry to a diamond.

2. Silicons conductivity increases as temperature increases.

3. Periodicity can be used to understand why doping with an element with oneextra valence electron converts silicon into an n-type semiconducting (negativecharge carrying) material, while doping with an element with one less valenceelectron converts silicon into a p-type semiconducting (positive chargecarrying) material. Junctions between n-doped and p-doped materials can beused to control electron flow, and thereby are the basis o modern electronics.


LO 2.29Te student can create a representation o a covalent solid that

shows essential characteristics o the structure and interactions present in thesubstance. [SeeSP 1.1]

LO 2.30Te student is able to explain a representation that connects propertieso a covalent solid to its structural attributes and to the interactions present at theatomic level. [SeeSP 1.1, 6.2, 7.1]

Essential knowledge 2.D.4: Molecular solids with low molecular weightusually have low melting points and are not expected to conductelectricity as solids, in solution, or when molten.

a. Molecular solids consist o nonmetals, diatomic elements, or compounds ormedrom two or more nonmetals.

b. Molecular solids are composed o distinct, individual units o covalently bondedmolecules attracted to each other through relatively weak intermolecular orces.

1. Molecular solids are not expected to conduct electricity because their electronsare tightly held within the covalent bonds o each constituent molecule.

2. Molecular solids generally have a low melting point because o the relativelyweak int

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