Post on 12-Mar-2020
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Regents&Chemistry:&Mr.&Palermo&& &
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Notes:&&Unit&4:&Atomics&& & & && & & && & & && & & && & &
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Key$Ideas$&
• The&modern&model&of&the&atom&has&evolved&over&a&long&period&of&time&through&the&work&of&many&scientists.(3.1a)&
• Each&atom&has&a&nucleus,&with&an&overall&positive&charge,&surrounded&by&one&or&more&negatively&charged&electrons.&(3.1b)&
• Subatomic&particles&contained&in&the&nucleus&include&protons&and&neutrons.&(3.1c)&• The&proton&is&positively&charged,&and&the&neutron&has&no&charge.&The&electron&is&negatively&
charged.(3.1d)&• Protons&and&electrons&have&equal&but&opposite&charges.&The&number&of&protons&equals&the&number&of&
electrons&in&an&atom.&(3.1e)&• The&mass&of&each&proton&and&each&neutron&is&approximately&equal&to&one&atomic&mass&unit.&An&
electron&is&much&less&massive&than&a&proton&or&a&neutron.&(3.1f)&• The&number&of&protons&in&an&atom&(atomic&number)&identifies&the&element.&The&sum&of&the&protons&
and&neutrons&in&an&atom&(mass&number)&identifies&an&isotope.&Common¬ations&that&represent&isotopes&include:&14C,&14C,&carbonL14,&CL14.&(3.1g)&
• In&the&waveLmechanical&model&(electron&cloud&model),&the&electrons&are&in&orbitals,&which&are&defined&as&the®ions&of&the&most&probable&electron&location&(ground&state).&(3.1h)&
• Each&electron&in&an&atom&has&its&own&distinct&amount&of&energy.&(3.1i)&• When&an&electron&in&an&atom&gains&a&specific&amount&of&energy,&the&electron&is&at&a&higher&energy&
state&(excited&state).&(3.1j)&• When&an&electron&returns&from&a&higher&energy&state&to&a&lower&energy&state,&a&specific&amount&of&
energy&is&emitted.&This&emitted&energy&can&be&used&to&identify&an&element.&(3.1k)&• The&outermost&electrons&in&an&atom&are&called&the&valence&electrons.&In&general,&the&number&of&
valence&electrons&affects&the&chemical&properties&of&an&element.&(3.1l)&• Atoms&of&an&element&that&contain&the&same&number&of&protons&but&a&different&number&of&neutrons&are&
called&isotopes&of&that&element.&(3.1m)&• The&average&atomic&mass&of&an&element&is&the&weighted&average&of&the&masses&of&its&naturally&
occurring&isotopes.&(3.1n)&• The&placement&or&location&of&elements&on&the&Periodic&Table&gives&an&indication&of&physical&and&
chemical&properties&of&that&element.&The&elements&on&the&Periodic&Table&are&arranged&in&order&of&increasing&atomic&number.&(3.1y)&
• For&Groups&1,&2,&and&13L18&on&the&Periodic&Table,&elements&within&the&same&group&have&the&same&number&of&valence&electrons&(helium&is&an&exception)&and&therefore&similar&chemical&properties.&(3.1z)&
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UNIT 4: ATOMICS WWW.MRPALERMO.COM
LESSON 4.1: ATOMIC THEORY
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Objective: By the end of this video you will be
able to:
! Describe how the modern model of the atom has evolved over a long period of time through the work of many scientists
! Relate experimental evidence to models of the atom
! Describe in detail Rutherford’s Experiment and the conclusions he made
Democritus (460-370 B.C.)
• His Model of the Atom: - Atom is the smallest piece that any
substance can be broken down into.
Dalton (1808)
• His Model of Atom: - All elements composed of tiny particles called
ATOMS - Atoms of same element are identical; atoms
of different elements are different
Dalton’s Model: Solid indestructible sphere
J. J. Thompson (1897)
• Discovered ELECTRONS using a cathode ray tube.
• His Model of the Atom: - “plum pudding” model - Atom is positively charged with negative
electrons “stuck” in it.
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Cathode Ray Tube (CRT)
• A Vacuum tube where a beam of electrons pass through from left to right.
• Thomson used it to discover electrons, - Concluded they are negatively charged.
CRT Television Check Your Understanding:
! Describe how the modern model of the atom has evolved over a long period of time through the work of many scientists
! Relate experimental evidence to models of the atom
Ernest Rutherford (1911)
• Discovered the NUCLEUS • His Model of the Atom: - Small dense positive nucleus - Atom is mostly empty space
Rutherford’s Gold Foil Experiment
The experiment: • Shot positively
charged alpha particles at gold foil.
The Result: • Most particles
went straight through.
• A few were deflected.
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His Conclusion: (you must know these)
1. Atom is mostly empty space 2. Small dense positive center (nucleus)
Example:
When alpha particles are used to bombard gold foil, most of the alpha particles pass through undeflected. This result indicates that most of the volume of a gold atom consists of ____.
1. a nucleus 2. neutrons 3. protons 4. unoccupied space
Check Your Understanding:
! Describe in detail Rutherford’s Experiment and the conclusions he made
MODERN THEORIES
Niels Bohr (1913)
• His Model of the Atom: • Electrons travel around the nucleus in
well-defined paths called ORBITS (like planets in a solar system)
• Electrons in different orbits possess different amounts of ENERGY.
Wave-Mechanical Model (present day model)
• Discovery: Can only determine the probability of finding an electron
• Model of the Atom: - Electrons found in ORBITALS
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Check Your Understanding:
! Describe how the modern model of the atom has evolved over a long period of time through the work of many scientists
! Relate experimental evidence to models of the atom
You should be able to:
! Describe how the modern model of the atom has evolved over a long period of time through the work of many scientists
! Relate experimental evidence to models of the atom
! Describe in detail Rutherford’s Experiment and the conclusions he made
LESSON 4.2: SUBATOMIC PARTICLES
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Objective: By the end of this video you will be
able to:
! Identify the subatomic particles of an atom (proton, neutron, and electron)
! Determine the number of protons, neutrons, electrons, nucleons and nuclear charge in a neutral atom
Name: Symbol Charge Mass
Proton (located in the nucleus)
p+ +1 1amu
Neutron (located in the nucleus)
n0
0 1amu
Electron (located outside the nucleus)
e- -1 1/1836 amu
Subatomic Particles
1 amu = 1/12th mass of a carbon-12 atom
amu = atomic mass unit
The Parts of the atom
Nucleons = (protons + neutrons)
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Check Your Understanding:
! Identify the subatomic particles of an atom (proton, neutron, and electron)
Atomic Number
" Equal to the number of protons " Every element has its own atomic
number " How periodic table is arranged
C 6
Mass Number
" Equal to the sum of the protons and the neutrons (whole number)
" Can be written as carbon-12
C 12 To find: # of protons
• Look up atomic number on Periodic Table
• Ex. Lithium has 3 protons
To find: # of electrons
• Equal to the # of protons in a neutral atom
• Ex. Lithium has 3 electrons
To find: # of neutrons
• Protons + Neutrons = Mass • # of neutrons = mass # - number of
protons • Ex. Lithium has 4 neutrons (7 – 3) = 4
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Check Your Understanding:
! Determine the number of protons, neutrons, electrons in a neutral atom
To find: Nuclear Charge
• Equal to the number of protons
• Ex. Lithium has a +3 nuclear charge
Example: Fill in the table
Element Atomic # Mass # # of protons # of neutrons
# of electron
s
Carbon (C)
Check Your Understanding:
! Determine the number of nucleons and nuclear charge in a neutral atom
You should be able to:
! Identify the subatomic particles of an atom (proton, neutron, and electron)
! Determine the number of protons, neutrons, electrons, nucleons and nuclear charge in a neutral atom LESSON 4.3: IONS
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Objective: By the end of this video you will be
able to:
! Determine the number of protons, neutrons, and electrons in an ion
Ions
• Charged particles • Formed when atoms gain or lose
electrons
caTion:
• The atom loses e- becomes positively charged
• Ex. Na+
7 +
7 -
7 +
6 -
aNion:
• the atom becomes negatively charged
• Ex. Cl-
17 +
17 - 18 -
17 +
Example:
Element Atomic #
Mass #
p n e
Fe
Fe3+ 26
26 56
56
26
26
26
23
30
30
Example:
Element Atomic #
Mass #
p n e
Br
Br1-
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Check Your Understanding:
! Determine the number of protons, neutrons, and electrons in an ion
You should be able to:
! Determine the number of protons, neutrons, and electrons in an ion
LESSON 4.4: ISOTOPES & AVERAGE ATOMIC MASS
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Objective: By the end of this video you will be
able to:
! Differentiate between atomic number, mass number, and (average) atomic mass
! Calculate the number of neutrons in an isotope
! Calculate the (average) atomic mass for all isotopes of an element
Isotopes
• Elements that have the same atomic number but different mass (different # of neutrons)
Isotope Symbols
• Show the mass of isotope • Same atomic #, different mass # • Ex. isotope symbol of element X
X Mass #
Atomic #
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Common Isotopes of Hydrogen
Name Symbol #p #e #n Mass
Protium H 1 1 0 1
Deuterium H 1 1 1 2
Tritium H 1 1 2 3
1
1
1
12
3
Example:
• The isotope symbol for Carbon-14
C
• How many neutrons does it have? 14 – 6 = 8
14
6
Mass # Proton #
Example: Write the isotope symbol for:
• Oxygen-17
O • How many neutrons does it have?
17
8
Check Your Understanding:
! Differentiate between atomic number, mass number, and (average) atomic mass
! Calculate the number of neutrons in an isotope
CALCULATING AVERAGE ATOMIC MASS
Why is atomic mass not a whole number?
• The atomic mass on the periodic table is a weighted average of the isotopes of the elements.
• The weighted atomic mass takes into account the relative abundances (amounts) of all the naturally occurring isotopes.
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Example of a general weighted average
Your grade in chemistry " 50% exams 85 " 10% quizzes 100. " 15% labs 95 " 25% HW/CW 80.
(50 x 85) + (10 x 100.) + (15 x 95) + (25 x 80.) =
100
= 87 avg.
Example: Determine avg atomic mass
Step 1: Multiply the mass of each isotope by its percent abundance then divide by 100
(19.78 x 10.013) + (80.22 x 11.009)
100
1.981 + 8.831 = 10.812 amu
Boron-10 19.78% 10.013 amu Boron-11 80.22% 11.009 amu
Example
Determine weighted atomic mass Potassium-39 93.12% 38.964 amu Potassium-41 6.88% 40.962 amu
Check Your Understanding:
! Calculate the (average) atomic mass for all isotopes of an element
You should be able to:
! Differentiate between atomic number, mass number, and (average) atomic mass
! Calculate the number of neutrons in an isotope
! Calculate the (average) atomic mass for all isotopes of an element
LESSON 4.5: BOHR DIAGRAMS
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Objective: By the end of this video you will be
able to:
! Construct Bohr diagrams for atoms and ions
Bohr Models
• How do electrons “orbit” the nucleus? • In energy levels • Each principal energy level: - is a fixed distance from the nucleus - can hold a specific number of electrons - has a definite amount of energy
• The greater the distance from the nucleus…the greater the energy of the electrons in it.
• The ORBITS are called principal energy levels or shells.
Increasing Energy
How many electrons can each shell hold?
• 2n2 • n = the period number from
reference table Ex. Max # of electrons in 1st shell is 2(1)2 = 2 e-
Drawing Bohr Diagrams
1. Look up electron configuration on Periodic table (if its an ion add/subtract the e- from the outermost energy level)
2. Draw a circle for nucleus and notate # of protons and neutrons in it.
3. Draw in energy levels and notate the # of electrons in each shell
Example: Bohr diagram of Mg
12 p+ 12 n0
2 e-
8 e-
2 e-
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Example: Bohr diagram of Mg+2
12 p+ 12 n0
2 e-
8 e-
Example: Bohr diagram of Ca+2
Check Your Understanding:
! Construct Bohr diagrams for atoms and ions
You should be able to:
! Construct Bohr diagrams for atoms and ions
LESSON 4.6: GROUND VS EXCITED STATE & BRIGHT LINE SPECTRUM
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Objective: By the end of this video you will be
able to:
! Differentiate between excited and ground state
! Explain how light is produced ! Identify substances based upon their
bright line spectra
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Ground State vs. Excited State
" Ground State- When electrons occupy the LOWEST available ENERGY LEVELS. (configuration on periodic table)
• Excited State- Electrons NO LONGER occupy the lowest available energy levels (different than electron configuration)
EXAMPLE: Possible Excited States for Sodium
Na (ground state)
Na (possible excited state)
Na (another possible
excited state)
Na (another possible
excited state)
2-8-1 2-7-2 2-6-3 2-5-4
How do you tell if the configuration is ground or excited state?
• Add up total # of electrons in configuration
• Determine element • If it matches element configuration on
periodic table = GROUND • If it doesn’t match = EXCITED
Example:
Identify the electron configuration as being ground state or excited state: 2-6-1
2+6+1 = 9 Fluorine Excited State
More Examples:
*****Remember when in excited state the total # of electrons DOES NOT change
Check Your Understanding:
! Differentiate between excited and ground state
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BRIGHT LINE SPECTRUM
Absorption
• Electrons absorb energy as they move to higher energy levels (excited state)
• This excited state is temporary and unstable.
Emission
• Electrons are negatively charged and therefore attracted to positive nucleus so eventually they fall back to ground state and give off the energy they absorbed as light energy.
Light
• The color of the light is determined by the amount of energy lost by the electron when it drops back to the ground state.
Electromagnetic Spectrum Example: Possible Ways an electron can fall back to ground state from 4th energy level.
1. From the 4th to the 1st energy level 2. From the 4th to the 3rd to the 1st energy
level 3. From the 4th to the 2nd to the 1st energy
level. 4. From the 4th to the 3rd to the 2nd to the 1st
energy level.
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Bright Line Spectra
• Each element has its own bright line spectra that is unique. (like a fingerprint)
• Can be used to identify an unknown mixture of gases.
Example: What Gases Comprise the Unknown?
Check Your Understanding:
! Explain how light is produced ! Identify substances based upon their
bright line spectra
You should be able to:
! Differentiate between excited and ground state
! Explain how light is produced ! Identify substances based upon their
bright line spectra
LESSON 4.7: LEWIS DOT DIAGRAMS
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Objective: By the end of this video you will be
able to:
! Construct Lewis dot diagrams for atoms and ions
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Lewis Dot Diagrams (electron dot diagrams)
• Only show VALENCE ELECTRONS • Valence shell: outer most shell of an
atom that contains electrons • Valence electrons: electrons that
occupy the valence shell (last number in electron configuration)
Steps for drawing dot diagrams:
1. Draw the elements symbol 2. Locate valence electron # (last
number of electron configuration) 3. Pair the first 2 electrons they deal out
any remaining one at a time to other 3 sides.
Example: Draw dot diagram for Carbon
C
Example: Draw dot diagram of Na
Na
Example: Draw dot diagram of Al
Al
Check Your Understanding:
! Construct Lewis dot diagrams for atoms
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Lewis Diagrams: Ions
1. Draw brackets around the element symbol
2. Write charge of ion outside bracket on top right corner of symbol
3. Positive ions no dots 4. Negative ions 8 dots Na
Na+ = 2-8
[ ] +
Example: K+
• Remove 1 electron from the valence shell of K
Example: S-2
• Add 2 electrons to the 6 that S normally has in its valence shell
Example: P and P-3
Check Your Understanding:
! Construct Lewis dot diagrams for ions
You should be able to:
! Construct Lewis dot diagrams for atoms and ions