Gen Chem PR MCATs_1

7/29/2019 Gen Chem PR MCATs_1

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General ChemistryGeneral ChemistryReview for the MCATReview for the MCAT

Dr. Paul A. J ellissDr. Paul A. J elliss

Monsanto Hall 114Monsanto Hall 114

(314) 977(314) 977--28342834

[email protected]@slu.edu

MCATMCATMCAT


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The MCAT: Basic StructureThe MCAT: Basic StructureVerbal Reasoning:Verbal Reasoning:

85 minutes, 65 questions.85 minutes, 65 questions.

Physical SciencesPhysical Sciences Physics &Physics & Gen. Chem.Gen. Chem.::

100 minutes, 77 questions.100 minutes, 77 questions.Writing Sample:Writing Sample:

30 minutes, 2 essays.30 minutes, 2 essays.

Biological SciencesBiological Sciences Organic & Biology:Organic & Biology:

100 minutes, 77 questions.100 minutes, 77 questions.

MCATMCATMCAT


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The Essentials for ClassThe Essentials for Class

A functional brain:A functional brain:

Eye(s) & Ear(s):Eye(s) & Ear(s):

not yet turned to mush?not yet turned to mush?

it might after this.it might after this.

preferably attached to aforementioned brain.preferably attached to aforementioned brain.

MCATMCATMCAT

Pen/pencil & notepaper:Pen/pencil & notepaper:

to write stuff down when I suggest,to write stuff down when I suggest, e.ge.g. examples.. examples. well try to make this at least a bit interactive towell try to make this at least a bit interactive to

keep you awake.keep you awake.

where else would you rather be early on a coldwhere else would you rather be early on a coldFebruary Saturday morning?February Saturday morning?


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What can we do in 6 hours?What can we do in 6 hours?

MCATMCATMCAT

No way can we cover absolutely everything fromNo way can we cover absolutely everything from

two semesters of general chemistry.two semesters of general chemistry. would you really want to relive that entire nightmarewould you really want to relive that entire nightmare

anyway?anyway?

We can look at key concepts from gen. chem. andWe can look at key concepts from gen. chem. andtry some examples which are MCATtry some examples which are MCAT--relevant.relevant.

Most importantly, RELAX!Most importantly, RELAX! but dont overbut dont over--do it.do it.

you will learn and test better under moderate anxiety.you will learn and test better under moderate anxiety.

Freaking out wont help!Freaking out wont help!


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General Chemistry on theGeneral Chemistry on the

MCATMCAT

Intermingled with physics in a PhysicalIntermingled with physics in a PhysicalSciences section (total 77 questions in 100Sciences section (total 77 questions in 100minutes).minutes).

~75 seconds per question.~75 seconds per question.

Some passages, some free standingSome passages, some free standing

questions: consider doing the latter first.questions: consider doing the latter first.Immediately following the verbal sectionImmediately following the verbal sectionbefore lunch.before lunch.

MCATMCATMCAT


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Back to the Basics:Back to the Basics:

Atomic StructureAtomic Structure

Atom: smallest unit of any element.Atom: smallest unit of any element.

Subunits:Subunits:protonsprotons,, neutronsneutrons,, electronselectrons::

protons and neutrons areprotons and neutrons are neucleonsneucleons..Atomic numberAtomic number((ZZ): proton number:): proton number:

identifies element, X.identifies element, X. charge ofcharge of+1+1..

mass of ~1mass of ~1 amuamu (1.66(1.66 10102727 kg).kg).


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Back to the Basics:Back to the Basics:

Atomic StructureAtomic Structure

Mass numberMass number((AA): mass of the atom.): mass of the atom.

AA == ZZprotonsprotons ++ NN neutronsneutrons == nucleonsnucleons..

NeutronsNeutrons: same mass as protons, no charge.: same mass as protons, no charge.Written as superscript before the elementWritten as superscript before the element

symbol:symbol:

AAZZ XX

##electronselectrons == ZZ in ain a neutralneutral atom!atom!


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Isotopes, Atomic Weight, andIsotopes, Atomic Weight, and

IonsIons

Atomic weight (not atomic mass)Atomic weight (not atomic mass)whats thewhats the

difference?difference?

Weighted average of masses of naturallyWeighted average of masses of naturally

occurring isotopes.occurring isotopes.

Ions:Ions: gaingain ororlossloss of electronsof electronsanionanion ororcationcation..

77 99

What is anWhat is an isotopeisotope??

Two atoms of the same element that differ inTwo atoms of the same element that differ intheir number of neutrons:their number of neutrons:

44Be andBe and 44Be.Be.


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Average Atomic WeightAverage Atomic WeightElement X has two isotopes of atomic massElement X has two isotopes of atomic mass

38.6 and 42.6 in 1:3 relative abundance.38.6 and 42.6 in 1:3 relative abundance.

What is the atomic weight of X?What is the atomic weight of X?

42.642.6

41.741.7

40.640.6

39.739.7


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Isotopes, Atomic Weight, andIsotopes, Atomic Weight, and

IonsIons ExampleExampleAn atom contains 16 protons, 17 neutrons,An atom contains 16 protons, 17 neutrons,and 18 electrons. Which of the followingand 18 electrons. Which of the followingbest indicates this atom?best indicates this atom?

3333ClCl

3434

ClCl

3333SS22

3434SS22


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Quantum Numbers:Quantum Numbers:

Electron Zip CodeElectron Zip Code

What is the purpose of quantum numbers?What is the purpose of quantum numbers?Quantum numbers designate a unique zipQuantum numbers designate a unique zipcode for each electron in an energy level.code for each electron in an energy level.

No two can have same zip code.No two can have same zip code.

How many quantum numbers in a zip code?How many quantum numbers in a zip code?

One zip codeOne zip code four quantum numbers.four quantum numbers.

shellshell,, subshellsubshell,, orbitalorbital,, spinspin..


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The First Quantum NumberThe First Quantum NumberWhat does it designate? What is its symbol?What does it designate? What is its symbol?

Principal quantum number designates thePrincipal quantum number designates the shellshell(symbol is(symbol is nn).).

Related to the size and energy of an orbital (aRelated to the size and energy of an orbital (athree dimensional region around the nucleus inthree dimensional region around the nucleus inwhich the electron is likely to be found).which the electron is likely to be found).

What are the possible values?What are the possible values?

nn= 1, 2, 3, 4, 5... (higher values are higher in= 1, 2, 3, 4, 5... (higher values are higher in

energy and farther from nucleus).energy and farther from nucleus).


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The Second Quantum NumberThe Second Quantum NumberWhat does it designate? Symbol?What does it designate? Symbol?

SubshellSubshell number (symbol isnumber (symbol is ll) describes shape) describes shapeof electrons orbital.of electrons orbital.

Values?Values?ll = 0, 1, 2,= 0, 1, 2,nn1 (If1 (Ifnn= 3, then= 3, then ll = 0, 1, or 2).= 0, 1, or 2).

ss,,pp

,,dd

, and, and

ff

subshellssubshells

correspond tocorrespond to

ll

values ofvalues of

0, 1, 2, and 3 respectively.0, 1, 2, and 3 respectively.

SubshellsSubshells have shapehave shapewhat are they?what are they?


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The Second Quantum NumberThe Second Quantum Number

Shapes mnemonic easy to remember:Shapes mnemonic easy to remember:

ss is foris forssphericalpherical dd is foris forddaisyaisy

pp is foris forppeanuteanut ffis foris forff------ed up!ed up!


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The Third Quantum NumberThe Third Quantum NumberWhat does it designate? Symbol?What does it designate? Symbol?

OrbitalOrbital number (symbol isnumber (symbol is mmll ) describes the) describes thethree dimensional orientation of an orbital.three dimensional orientation of an orbital.

Values?Values?Value ofValue ofmmll ==l...0...l...0...++ll inclusive.inclusive.

IfIfll = 0, then= 0, then mmll = 0= 0

IfIfll = 1, then= 1, then mmll ==1, 0, 11, 0, 1

IfIfll = 2, then= 2, then mmll ==2,2,1, 0, 1, 21, 0, 1, 2


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The Fourth Quantum NumberThe Fourth Quantum NumberWhat does it designate? Symbol?What does it designate? Symbol?

SpinSpin number (symbol isnumber (symbol is mmss ) designates) designates

electrons intrinsic magnetism.electrons intrinsic magnetism.

Values?Values?

Value ofValue ofmmss == ++ oror only.only.11

22

11

22

Every orbital can accommodate 2 electrons.Every orbital can accommodate 2 electrons.If an orbital is full, the electrons it holds areIf an orbital is full, the electrons it holds arespinspin--paired.paired.


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Assigning Quantum Numbers: RulesAssigning Quantum Numbers: Rules

AufbauAufbauprinciple: What is it?principle: What is it?

Electrons occupy the lowest energyElectrons occupy the lowest energy orbitalsorbitals

available:available:

HundsHunds Rule: Basic point?Rule: Basic point?

Electrons in sameElectrons in same subshellsubshell occupy availableoccupy available

orbitalsorbitals singly before pairing up.singly before pairing up.

PauliPauli Exclusion Principle: Think exclusion?Exclusion Principle: Think exclusion?

No two electrons can have same set of fourNo two electrons can have same set of fourquantum numbers.quantum numbers.

11ss--22ss--22pp--33ss--33pp--44ss--33dd--44pp--55ss--44dd--55pp--66ss--44ff--55dd--

66pp--77ss--55ff--66dd--77pp--


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1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d

7s 7p

Assigning Quantum Numbers: RulesAssigning Quantum Numbers: Rules

Fill

in

orde

rofinc

reasing

Fill

in

orde

rofinc

reasing

nn

+

+ll


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Ground State ElectronGround State Electron

ConfigurationsConfigurations

Use previous three rules to write.Use previous three rules to write.How would oxygen look?How would oxygen look?

11ss

22

22ss

22

22pp

44

Frequently, shortcut designations are usedFrequently, shortcut designations are used

instead of writing out the entire configurationinstead of writing out the entire configurationP for example:P for example:

[Ne]3[Ne]3ss22

33pp33


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Electron Configurations:Electron Configurations:

AnomaliesAnomaliesSometimes the anticipated electronSometimes the anticipated electron

configuration is not the actual one: stabilityconfiguration is not the actual one: stabilitythroughthrough filledfilled ororhalfhalf--filledfilled subshellssubshells..

What are some exceptions?What are some exceptions?The exceptions: Cr, Cu, Mo, Ag, Au.The exceptions: Cr, Cu, Mo, Ag, Au.

What is Cr expected?What is Cr expected?[Ar]4[Ar]4ss2233dd44

But what is it really?But what is it really?Cr actual: [Ar]4Cr actual: [Ar]4ss1133dd55


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Electron Configurations: IonsElectron Configurations: IonsAnions accommodate the gained electrons inAnions accommodate the gained electrons in

the first available orbital with the lowestthe first available orbital with the lowestavailable energy.available energy.

F (F (ZZ=9) has=9) has configconfig. 1. 1ss2222ss2222pp55 while Fwhile F hashasconfigconfig. 1. 1ss2222ss2222pp66

configuration exactly likeconfiguration exactly likeNeNe (F(F andandNeNe are calledare called

isoelectronicisoelectronic).).

isoiso-- = same,= same, --electronic = configuration.electronic = configuration.


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2222

Electron Configurations: IonsElectron Configurations: IonsCationsCations lose electrons from the most unstablelose electrons from the most unstable

orbital: How would Liorbital: How would Li++ look?look?Li (Z = 3) hasLi (Z = 3) has configconfig. 1. 1ss2222ss11 and Liand Li++ hashasconfigconfig. 1. 1ss22

How about TiHow about Ti++??

For transition metals, the valenceFor transition metals, the valence ss electronselectrons

are always lost first, before anyare always lost first, before any dd electrons.electrons.TiTi++ ((ZZ= 22) expected [Ar]3= 22) expected [Ar]3dd1144ss22but Tibut Ti++

actually: [Ar]3actually: [Ar]3dd22

44ss11


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ExamplesExamples

Which of the following gives the electronWhich of the following gives the electron

configuration of an aluminum atom?configuration of an aluminum atom?

11ss2222ss2222pp11

11ss2222ss2222pp22

11ss2222ss2222pp6633ss2233pp11

11ss2222ss2222pp6633ss2233pp22


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ExamplesExamples

What is the electron configuration of an atomWhat is the electron configuration of an atom

of copper?of copper?

Remember, Cu is an exception!Remember, Cu is an exception!Expected: [Ar]3Expected: [Ar]3dd9944ss22

Actual: [Ar]3Actual: [Ar]3dd101044ss11

MoralMoral: beware of stability in transition metals!: beware of stability in transition metals!


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Diamagnetic and ParamagneticDiamagnetic and ParamagneticAtomsAtoms

DiamagneticDiamagnetic: all electrons are spin paired: all electrons are spin paired

(even number of electrons):(even number of electrons):

atom repelled by a magnetic field.atom repelled by a magnetic field.

ParamagneticParamagnetic: not all electrons are spin: not all electrons are spin--paired:paired:

atom attracted by a magnetic field.atom attracted by a magnetic field.

Know the differenceKnow the differencethese are easy points!these are easy points!


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l l dEl E L l d


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Electron Energy Levels andElectron Energy Levels and

SpectraSpectraFormula for the energy of a photon?Formula for the energy of a photon?

EE == hh== hchc//define the terms!define the terms! Plancks constant,Plancks constant, hh= 6.63= 6.63 10103434 JJ..ss

EmissionEmission vsvs. absorption spectra: Whats the. absorption spectra: Whats thedifference?difference?

EmissionEmission: electrons dropping to lower energy: electrons dropping to lower energy

levels emit light of specific frequencies which arelevels emit light of specific frequencies which areseparated into bright lines by a prism.separated into bright lines by a prism.

AbsorptionAbsorption: specific frequencies of white light are: specific frequencies of white light are

absorbed by gaseous element based on differencesabsorbed by gaseous element based on differencesbetween quantized energy levelsbetween quantized energy levelsdark bands.dark bands.


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Electromagnetic SpectrumElectromagnetic Spectrum

From lowest to highest energy level?From lowest to highest energy level?

RadiowavesRadiowaves microwavesmicrowaves infraredinfrared

visible lightvisible light ultravioletultraviolet XX--raysrays gammagamma

rays.rays.Visible light, from lowest to highest frequency?Visible light, from lowest to highest frequency?

RedRed orangeorange yellowyellow greengreenblueblue indigoindigo violetviolet

RROOYYGGBBIIVV

Trends are important, not values.Trends are important, not values.


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Nuclear Structure and DecayNuclear Structure and Decay

Protons and neutrons held together by strongProtons and neutrons held together by strong

nuclear force which overcomes the electricalnuclear force which overcomes the electricalrepulsion between the protons.repulsion between the protons.

What is radioactive decay?What is radioactive decay?

Unstable nuclei undergo a transformation byUnstable nuclei undergo a transformation byaltering the number and ratio of protons andaltering the number and ratio of protons and

neutrons or lowering their energy.neutrons or lowering their energy.What are parent and daughter nuclei?What are parent and daughter nuclei?

Anyone done the different types in class?Anyone done the different types in class?


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Alpha Decay:Alpha Decay: An alpha particle, denoted byAn alpha particle, denoted by , consists of, consists of22protonsprotons andand 2 neutrons2 neutrons, equivalent to a He, equivalent to a He

nucleus, which is ejected.nucleus, which is ejected.

Alpha decay reduces the parents atomicAlpha decay reduces the parents atomic

number by 2 and mass number by 4.number by 2 and mass number by 4.

2102108484PoPo ++ 4422HeHe

ZZ ==2,2, AA ==44

2062068282PbPb


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Positron Decay:Positron Decay:

++

When unstable nucleus contains too fewWhen unstable nucleus contains too few

neutrons, it may convert a proton into a neutronneutrons, it may convert a proton into a neutronand positron (and positron (++particle) which is ejected:particle) which is ejected: 1111pp 1100nn ++

00+1+1ee

++

Positron is electrons antiparticlePositron is electrons antiparticleidentical toidentical toelectron, but charge is positive.electron, but charge is positive.

Atomic number of daughter nucleus is 1 lessAtomic number of daughter nucleus is 1 lessthan parent, but mass number same.than parent, but mass number same.1818

99FF ++00+1+1ee

++181888OO

ZZ ==1,1, AA = 0= 0


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Electron CaptureElectron Capture

Conversion of a proton into a neutron by anConversion of a proton into a neutron by an

unstable nucleus by capturing an electron (unstable nucleus by capturing an electron (ee))

from the closest shell:from the closest shell: 1111pp ++0011ee

1100nn

Atomic number of daughter nucleus is 1 lessAtomic number of daughter nucleus is 1 lessthan parent, but mass number samethan parent, but mass number samejust likejust like

positron emission.positron emission.

51512424Cr +Cr +

0011ee

51512323VV

ZZ ==1,1, AA = 0= 0


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Gamma Decay:Gamma Decay:

Nucleus in excited state (often after alpha orNucleus in excited state (often after alpha or

beta decay) emits energy in form of photons ofbeta decay) emits energy in form of photons of

electromagnetic radiation.electromagnetic radiation.

Gamma photons (Gamma photons (rays) have neither mass norrays) have neither mass norcharge, and their ejection changes neithercharge, and their ejection changes neither

atomic mass or number.atomic mass or number.

31311414SiSi

31311515P +P +

++

ZZ = 0,= 0, AA = 0= 0

31311515PP


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Radioactive Decay: ExampleRadioactive Decay: Example

Memory device:Memory device:

++ decay starts withdecay starts withprotonproton and makes it aand makes it a neutronneutron..

decay starts withdecay starts with neutronneutron and makes it aand makes it aprotonproton..


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Radioactive Decay: Half LifeRadioactive Decay: Half Life

What is a halfWhat is a half--life?life?

The time it takes for oneThe time it takes for one--half of some samplehalf of some sampleof radioactive substance to decay.of radioactive substance to decay.

Shorter half lives mean faster decay.Shorter half lives mean faster decay.Half life denoted byHalf life denoted by tt1/2.1/2.Make a chart to solve these problemsMake a chart to solve these problemsforgetforgetthe formula unless you do ethe formula unless you do e--functions in yourfunctions in yourhead!head!


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Radioactive Decay: Half LifeRadioactive Decay: Half Life

TimeTime Amount of SampleAmount of Sample

RemainingRemaining

00 100 %100 %

1 half1 half--lifelife tt1/21/2 1/2 = 50 %1/2 = 50 %

22 halfhalf--liveslives 22tt1/21/2 (1/2)(1/2)22 = 1/4 = 25 %= 1/4 = 25 %

33 halfhalf--liveslives 33tt1/21/2 (1/2)(1/2)33 = 1/8 = 12.5 %= 1/8 = 12.5 %

44 halfhalf--liveslives 44tt1/21/2

(1/2)(1/2)44 = 1/16 = 6.25 %= 1/16 = 6.25 %


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Half Life: ExampleHalf Life: Example

RadiolabeledRadiolabeled vitamin Bvitamin B--12 containing12 containingradioactive cobaltradioactive cobalt--58 is administered to diagnose58 is administered to diagnosea defect in a patients vitamin Ba defect in a patients vitamin B--12 absorption.12 absorption.If the halfIf the half--life is 72 days, approximately whatlife is 72 days, approximately what

percentage of the radioisotope will remain in thepercentage of the radioisotope will remain in thepatient a year later?patient a year later?

3 %3 %

5 %5 %

8 %8 %

10 %10 %


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The MoleThe Mole

Mole:Mole: amount of substanceamount of substance contains same #contains same #

of elementary entities as carbonof elementary entities as carbon--12 atoms in12 atoms inexactlyexactly12 g carbon12 g carbon--12.12.

AvogadroAvogadros constants constant,, NNAA

= 6.022= 6.022 10102323 molmol11..

Molar massMolar mass: mass (g) of 1 mole of substance.: mass (g) of 1 mole of substance.

# moles =mass (g)

molar mass (gmol1)


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Chemical CompoundsChemical Compounds

Chemical compoundChemical compound pure substance,pure substance,

can be broken into 2/more elements.can be broken into 2/more elements.MoleculeMolecule smallest unit of a compound,smallest unit of a compound,

still retains properties (formula unit forstill retains properties (formula unit forionic compounds).ionic compounds).

AtomAtom smallest unit of an element.smallest unit of an element.

Any compound always contains same %Any compound always contains same %composition by mass,composition by mass, e.g.e.g. iron (III) oxide:iron (III) oxide:

Fe = 69.9 %Fe = 69.9 % O = 30.1 %O = 30.1 %

i i l l


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Empirical FormulaEmpirical Formula

Find lowest multiple(s) of whole atomsFind lowest multiple(s) of whole atoms

22--step process:step process:

cc assume 100 g compound:assume 100 g compound:

dd convert numbers to lowest whole multiple(s):convert numbers to lowest whole multiple(s):

1 mol

55.9 g= 1.25 mol

Fe = 69.9 g

= 1.88 molO = 30.1 g

1.5 mol O

1.0 mol Fe

3 mol O

2 mol Fe= =

1 mol

16.0 g

Fe2O31.88 mol O

1.25 mol Fe


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Molecular FormulaMolecular Formula

For many (usually organic) compounds,For many (usually organic) compounds,

actual molecular formula usually notactual molecular formula usually notempirical (simplest ratio),empirical (simplest ratio), e.ge.g. glucose:. glucose:

Empirical: CHEmpirical: CH22OO molecular: Cmolecular: C66HH1212OO66

molecular mass

= integern

CCnnxxHHnnyyOOnnzzempirical mass

For glucoseFor glucose nn= 6= 6..


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Balanced Chemical EquationsBalanced Chemical Equations

Inorganic chemistryInorganic chemistry conservation of matterconservation of matter::

22HH22 + O+ O22 22HH22OO

Organic chemistry:Organic chemistry:

CC33HH88 + O+ O22 COCO22 + H+ H22OO

cc CC33HH88 + O+ O22 33COCO22 + H+ H22OO

dd CC33HH88 + O+ O22 33COCO22 ++ 44HH22OO

ee CC33HH88 ++ 55OO22 33COCO22 ++ 44HH22OO

Balance O lastBalance O lastwhywhy??

StoichiometricStoichiometric

coefficientscoefficients


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Types of Chemical ReactionTypes of Chemical Reaction

1.1. Precipitation reactions.Precipitation reactions.

2.2. Neutralization reactions.Neutralization reactions.3.3. GasGas--forming reactions.forming reactions.

4.4.

RedoxRedox

reactionreaction


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N t li ti R tiN t li ti R ti


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Neutralization ReactionsNeutralization Reactions

Strong acid + strong baseStrong acid + strong base salt + watersalt + water

HCl(HCl(aqaq) +) +NaOH(NaOH(aqaq)) NaCl(NaCl(aqaq) + H) + H22O(O(ll))

HH++(aq(aq) +) + ClCl((aqaq) +) +NaNa++(aq(aq) + OH) + OH((aqaq))

NaNa++(aq(aq) +) + ClCl((aqaq) + H) + H22O(O(ll))

Net ionic reactionNet ionic reaction:: HH++(aq(aq) + OH) + OH((aqaq)) HH22

O(O(ll))

Spectator ions


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RedoxRedox ReactionsReactions


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RedoxRedox ReactionsReactions

Reactions involving transfer of electronsReactions involving transfer of electrons

and changes in oxidation state.and changes in oxidation state.

FeFe2+2+(aq)(aq) FeFe3+3+(aq) + e(aq) + e

MnOMnO44((aqaq)) + 5e+ 5e MnMn2+2+(aq)(aq)

MnOMnO44((aqaq) + 5e) + 5e MnMn2+2+(aq)(aq) + 4H+ 4H22O(l)O(l)

MnOMnO44((aqaq) +) + 8H8H++(aq)(aq) ++ 55ee MnMn2+2+(aq) + 4H(aq) + 4H22O(l)O(l)

55FeFe2+2+(aq)(aq) 55FeFe3+3+(aq) +(aq) + 55ee

5Fe5Fe2+2+(aq) + MnO(aq) + MnO44((aqaq) + 8H) + 8H++(aq)(aq)

5Fe5Fe3+3+(aq)(aq) + Mn+ Mn2+2+(aq) + 4H(aq) + 4H22O(l)O(l)

reductantreductant

oxidantoxidant

Net ionic reactionNet ionic reaction


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Groups of the Periodic TableGroups of the Periodic Table


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PeriodsPeriods are horizontal rows.are horizontal rows.

GroupsGroups (families) are vertical columns.(families) are vertical columns.MetalsMetals,, nonmetalsnonmetals andand metalloidsmetalloids: which: which

are which?are which?

What are the electrons in an atomsWhat are the electrons in an atomsoutermost shell called?outermost shell called?

Valence electrons: primarily responsible forValence electrons: primarily responsible forchemical behavior.chemical behavior.


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The Octet RuleThe Octet Rule: What is an octet?: What is an octet?Great stability inGreat stability in nsns22npnp66 electronelectron

configuration.configuration.

All noble gases have a complete octet:All noble gases have a complete octet:

8 valence electrons.8 valence electrons.

One exception: what is it?One exception: what is it?


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Periodic Trends:Periodic Trends:


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Atomic and Ionic RadiusAtomic and Ionic RadiusWhat properties of an atom determine radius?What properties of an atom determine radius?

Radius is a function of total pull of protons onRadius is a function of total pull of protons on

valence electrons: what does the trend look like?valence electrons: what does the trend look like?

More protons to the right within a period meansMore protons to the right within a period meansstronger pullstronger pull smaller radiussmaller radius::

Number of shells doesnt change in a period.Number of shells doesnt change in a period.More shells downward within a group meansMore shells downward within a group means

more shieldingmore shielding larger radiuslarger radius..


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Lewis Dot StructuresLewis Dot Structures


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Anyone remember the rules?Anyone remember the rules?

Pay attention to valence electrons.Pay attention to valence electrons.

1.1. skeleton structureskeleton structure central atom (lowestcentral atom (lowest).).

2.2. total valence etotal valence e count (group #s).count (group #s).

3.3. # valence e# valence epairspairs = valence e= valence e/2./2.

4.4. make single covalent bonds.make single covalent bonds.

5.5. remaining pairsremaining pairs terminal atomsterminal atoms lone pairslone pairs (octet(octetrule!).rule!).

6.6. left over eleft over e central atom.central atom.

7.7. if still < 8 eif still < 8 e then turn lone pairthen turn lone pairbond pairbond pair

multiple bondsmultiple bonds (C, N, O, P, S).(C, N, O, P, S).

Lewis Dot Structures:Lewis Dot Structures:


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Formal ChargeFormal ChargeAnyone know what it is?Anyone know what it is?

Are atoms sharing valence electrons in theAre atoms sharing valence electrons in thebestbest way possible (formal charge = 0)?way possible (formal charge = 0)?

HCN or HNC? Only one is right evenHCN or HNC? Only one is right eventhough both satisfy the octet rule.though both satisfy the octet rule.

FC =FC =

VV

BB

LL

11

22 VV = # valence electrons (free atom)= # valence electrons (free atom)

BB = # bonding electrons= # bonding electrons

LL = # lone pair electrons= # lone pair electrons


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LewisDotStructure: ExamplesLewisDotStructure: Examples


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Lewis Dot Structure: ExamplesLewis Dot Structure: Examples

Which is the best Lewis structure for theWhich is the best Lewis structure for the

nitroniumnitronium ion, NOion, NO22++??

Polar Covalent BondsPolar Covalent Bonds


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Polar Covalent Bonds

Covalent bonding: shared electrons.Covalent bonding: shared electrons.

Polar covalent: unequal sharing.Polar covalent: unequal sharing.

A bond is polar if electron density betweenA bond is polar if electron density between

the atoms is uneventhe atoms is unevena function of what?a function of what?Dipole moment,Dipole moment, == erer..

Polar or not?Polar or not? CClCCl44HFOCSNOHFOCSNO33

X Y+ r


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Ionic BondsIonic Bonds


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What are they?What are they?

One atom gives a valence electron to theOne atom gives a valence electron to theother and electrostatic interaction holdsother and electrostatic interaction holds

atoms together.atoms together.Usually between aUsually between a metalmetal andand nonmetalnonmetal, but, but

always between two atoms with largealways between two atoms with large

electronegativityelectronegativity difference,difference, ..

NaClNaClKClKCletcetc..

VSEPR TheoryVSEPR Theory


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yy

Basic premise: electron pairs on a centralBasic premise: electron pairs on a centralatom try to move apart as far as possible.atom try to move apart as far as possible.

Electron group geometryElectron group geometry vsvs. molecular. moleculargeometry?geometry?

Electron group geometryElectron group geometry : electron groups: electron groups((bondingbonding andand nonbondingnonbonding) on center atom) on center atomdetermine geometric family.determine geometric family.

Molecular geometryMolecular geometry::bondingbondingpairs aroundpairs aroundcenter atom determine shape, more specific thancenter atom determine shape, more specific thanelectron groups.electron groups.

MoralMoral: determine family, then shape.: determine family, then shape.

VSEPR Theory: The FamiliesVSEPR Theory: The Families


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Electron GroupsElectron Groups Geometric FamilyGeometric Family

22 LinearLinear

33 TrigonalTrigonal PlanarPlanar44 TetrahedralTetrahedral

55 TrigonalTrigonal BipyramidalBipyramidal

66 OctahedralOctahedral


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VSEPR Theory: ExamplesVSEPR Theory: Examples


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8080

Draw/think about Lewis structures!Draw/think about Lewis structures!

Count electron groups around center atomCount electron groups around center atomforforfamilyfamily..

CountCount bondingbonding groups around center atom togroups around center atom tonarrow down family into molecularnarrow down family into molecularshapeshape..

multiple bond counts as one group.multiple bond counts as one group.

Dont memorize all of thisDont memorize all of thisvisualize!visualize! except geometry names (familiar?).except geometry names (familiar?).


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Solids and IntermolecularSolids and Intermolecular


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ForcesForcesDifferentiate between ionic, network, andDifferentiate between ionic, network, and

metallic solids.metallic solids.Ionic: electrostatic attractions (Ionic: electrostatic attractions (NaClNaCl, CaF, CaF22).).

Network: lattice of covalent bonds (diamond,Network: lattice of covalent bonds (diamond,quartz).quartz).

Metallic: covalent lattice of nuclei and innerMetallic: covalent lattice of nuclei and inner

electrons surrounded by cloud of electrons.electrons surrounded by cloud of electrons. What are conduction electrons?What are conduction electrons?

Solids and IntermolecularSolids and Intermolecular


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ForcesForcesIntermolecular forces are relatively weakIntermolecular forces are relatively weak

interactions between neutral/charged molecules.interactions between neutral/charged molecules.Four major types: what are they?Four major types: what are they?

IonIon--dipoledipole: polar molecules attracted to ions.: polar molecules attracted to ions.

DipoleDipole--dipoledipole: between positive and negative end of: between positive and negative end oftwo polar molecules.two polar molecules.

DipoleDipole--induced dipoleinduced dipole: permanent dipole induces: permanent dipole inducesdipole in nondipole in non--polar molecule.polar molecule.

London dispersion forcesLondon dispersion forces: instantaneous dipole: instantaneous dipoleinduces a dipole in neighboring noninduces a dipole in neighboring non--polar moleculepolar molecule(also(also VanVan derderWaalsWaals forces).forces).


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Phase Transitions: SummaryPhase Transitions: Summary


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Evaporation, condensation, fusion,Evaporation, condensation, fusion,

crystallization, sublimation, deposition:crystallization, sublimation, deposition:define!define!

Evaporation: liquid to gas.Evaporation: liquid to gas.

Condensation: gas to liquid.Condensation: gas to liquid.

Fusion (melting): solid to liquid.Fusion (melting): solid to liquid.

Crystallization (freezing): liquid to solid.Crystallization (freezing): liquid to solid.Sublimation: solid to gas.Sublimation: solid to gas.

Deposition: gas to solid.Deposition: gas to solid.

Phase Transitions: SummaryPhase Transitions: Summary


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GasGas liquidliquid solid: what happens to heat,solid: what happens to heat,

KE, and entropy?KE, and entropy?Heat released, internal KE decreases,Heat released, internal KE decreases,entropy decreases.entropy decreases.

SolidSolid liquidliquid gas: what happens to heat,gas: what happens to heat,KE, and entropy?KE, and entropy?

Heat absorbed, internal KE increases,Heat absorbed, internal KE increases,entropy increases.entropy increases.

Know the conceptual trends!Know the conceptual trends!


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Gases and KineticGases and Kinetic--MolecularMolecular

TheoryTheory


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TheoryTheory

What is the purpose of the theory?What is the purpose of the theory?Sets the conditions for an ideal gas.Sets the conditions for an ideal gas.

Normally, real gases operate like ideal gases,Normally, real gases operate like ideal gases,so these conditions can be applied toso these conditions can be applied to

understand gas behavior.understand gas behavior.

A good example of this application: the idealA good example of this application: the ideal

gas law.gas law.


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Ideal Gas LawIdeal Gas Law


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Describes behavior of gases followingDescribes behavior of gases following

kinetickinetic--molecular theory.molecular theory.What is the equation?What is the equation?

PVPV ==

nRTnRTdefine the terms.define the terms.Gas constantGas constant:: RR = 0.0821= 0.0821 LatmLatm molmol11KK11

Derivations of other laws from the idealDerivations of other laws from the ideal--gasgaslawlawthree proportionalities, two have names.three proportionalities, two have names.

Other POther P--VV--T Gas LawsT Gas Laws


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Volume proportional to temperature atVolume proportional to temperature at

constant pressureconstant pressurewhat law?what law?Charles LawCharles Law VV11//TT11 == VV22//TT22

Pressure inversely proportional to volume atPressure inversely proportional to volume atconstant temperatureconstant temperaturewhat law?what law?

Boyles LawBoyles Law PP11VV

11== PP

22VV

22Pressure proportional to temperature atPressure proportional to temperature at

constant volumeconstant volume PP11//TT11 == PP22//TT22


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IdealIdeal--Gas Law: ExampleGas Law: Example


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104104

How many atoms of helium are present in 11.2How many atoms of helium are present in 11.2

liters of the gas at a pressure of 1liters of the gas at a pressure of 1 atmatm andandtemperature of 273 K?temperature of 273 K?

3.013.01

10102323

6.026.02 10102323

1.201.20 10102323

Cannot be determined from informationCannot be determined from information

given.given.


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Gen Chem PR MCATs_1

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