Atomic Structure and the Quantum Model

Chapter 7Chapter 7
Atomic StructureAtomic Structure pppp

7.1 Electromagnetic Radiation7.1 Electromagnetic Radiation
LightLight is made up ofis made up of electromagneticelectromagnetic
radiationradiation..
Waves of electric and magnetic fields atWaves of electric and magnetic fields at
right anglesright angles to each other.to each other.
LD 1: 4-1 Electromagnetic radiationLD 1: 4-1 Electromagnetic radiation

3
Electromagnetic Radiation
Mutually propagating electric and magnetic fields, at
right angles to each other, traveling at the speed of light c

4
Parts of a wave
Wavelength
Amplitude
Origin
Crest
Trough

5
Parts of Wave
Origin - the base line of the energy.
Crest - high point on a wave
Trough - Low point on a wave
Amplitude - distance from origin to crest
Wavelength - distance from crest to
crest
Wavelength - is abbreviated λ Greek
letter lambda.

Parts of a waveParts of a wave
λ
Wavelength
Frequency = number of cycles in one second
Measured in hertz 1 hertz = 1 cycle/second

7
Frequency
The number of waves that pass a
given point per second.
Units are cycles/sec or hertz (Hz)
Abbreviated ν the Greek letter nu
c = λν

8
Frequency and wavelength
Are inversely related
As one goes up the other goes down.
Speed is constant! (Tricky)
In a vacuum it is 3.00 x 108
m/s or
3.00 x 1010
cm/s
Memorize both.
Also, 1 m = 1 x 109
nm = 1 x 1010
Å
(angstrom)

Figure 7.1
The Nature
of Waves

1
Kinds of EM wavesKinds of EM waves
There are manyThere are many
differentdifferent λλ andand νν
Radio waves, microwaves, x raysRadio waves, microwaves, x rays
and gamma rays are all examples.and gamma rays are all examples.
Light is only the part our eyes canLight is only the part our eyes can
detect.detect.
Gamma
Rays
Radio
waves

12
Radio
waves
Micro
waves
Infrared
.
Ultra-
violet
X-
Rays
Gamma
Rays
Low
energy
High
energy
Low
Frequency
High
Frequency
Long
Wavelength
Short
Wavelength
Visible Light

13
Electromagnetic Spectrum
Which has longer λ, ultraviolet or gamma rays?
UV rays
Which has shorter wavelength, microwave or infrared?
Microwave

4
Figure 7.2Figure 7.2
Classification of Electromagnetic RadiationClassification of Electromagnetic Radiation

5
The speed of lightThe speed of light
In a vacuum is 2.998 x 10In a vacuum is 2.998 x 1088
m/s = cm/s = c
cc == λλνν
What is theWhat is the wavelengthwavelength of light with aof light with a
frequencyfrequency 5.89 x 105.89 x 1055
Hz? Ans . . .Hz? Ans . . .
509 m509 m (using 2.998 x 10(using 2.998 x 1088
m/s)m/s)
What is theWhat is the frequencyfrequency of blue light withof blue light with
aa wavelengthwavelength ofof 484 nm484 nm??
6.19 x 106.19 x 101414
HzHz

6
7.2 The Nature of Matter7.2 The Nature of Matter
In 1900In 1900 Matter and energy were seen asMatter and energy were seen as
different from each other in fundamentaldifferent from each other in fundamental
ways.ways.
It was thought that matter was particles.It was thought that matter was particles.
It was thought that energy could come inIt was thought that energy could come in
waves,waves, with any frequencywith any frequency..
Max Planck found the cooling of hotMax Planck found the cooling of hot
objects couldobjects could notnot be explained by viewingbe explained by viewing
energy as a wave.energy as a wave.

17
The Photoelectric Effect
Photoelectric Effect - the emission of
electrons from a metal when light
shines on it.

18
Tr 19 Fig 4.3 p. 93 Photoelectric Effect

19
The Photoelectric Effect Problem
What was predicted . . .
Wave theory said light of any ν would have
enough energy to eject an electrons.
What was observed . . .
For a given metal, no e- are emitted if ν is below
a certain frequency no matter how long the light
shines.
The explanation . . .

20
Light is a Particle as well as a Wave
Energy is quantized.
Light is energy
Light must be quantized
These smallest pieces of light are
called photons.
Energy and frequency are directly
related.

1
Energy is QuantizedEnergy is Quantized
Planck foundPlanck found ∆∆E came in chunks with sizeE came in chunks with size
hhνν
∆∆E = nhE = nhνν
where n is an integerwhere n is an integer
and h isand h is Planck’s constantPlanck’s constant
h = 6.626 x 10h = 6.626 x 10-34-34
J•sJ•s
1 joule = 1 Kg m1 joule = 1 Kg m22
/s/s22
(know this!)(know this!)
these packets of hthese packets of hνν are calledare called quantaquanta
(singular = quantum)(singular = quantum)

2
Einstein is nextEinstein is next
He said electromagnetic radiation isHe said electromagnetic radiation is
quantizedquantized in particles calledin particles called photonsphotons..
Each photon has energy E= hEach photon has energy E= hνν == hc/hc/λλ
Combine this with E =Combine this with E = mcmc22
mcmc22
== hc/hc/λλ
You get theYou get the apparentapparent massmass of a photon.of a photon.
mm = h / (= h / (λλc)c)

3
Which is Energy?Which is Energy?
Is energy a wave like light, or a particle?Is energy a wave like light, or a particle?
Both.Both.
Concept is called the Wave-ParticleConcept is called the Wave-Particle
duality.duality.
What about the other way, is matter aWhat about the other way, is matter a
wave?wave?
YesYes

4
Electromagnetic RadiationElectromagnetic Radiation

5
Matter as a waveMatter as a wave
Using the velocity v instead of theUsing the velocity v instead of the
speed of light c we get. . .speed of light c we get. . .
De Broglie’s equationDe Broglie’s equation λλ = h/mv= h/mv
Mass in this equation is inMass in this equation is in kgkg (not g!)(not g!)
Remember this! You have an onlineRemember this! You have an online
HW question that uses this equation.HW question that uses this equation.
Can calculate the wavelength of anCan calculate the wavelength of an
object.object.

6
ExamplesExamples pppp
The laser light of a CD player is 7.80 x 10The laser light of a CD player is 7.80 x 1022
m.m.
What is theWhat is the frequencyfrequency? Answer . . .? Answer . . .
C =C = λλ νν soso νν = c/= c/λλ == 3.84 x 103.84 x 1055
HzHz
What is theWhat is the energyenergy of a photon of this light?of a photon of this light?
E = hE = hνν E = 2.55 x 10E = 2.55 x 10-28-28
JJ
What is the apparent mass for this photon?What is the apparent mass for this photon?
apparent mass = h/apparent mass = h/ λλc = 2.83 x10c = 2.83 x10-45-45
kgkg
What is the energy of a mole of photons?What is the energy of a mole of photons?
E of mole in (c) above = (h/E of mole in (c) above = (h/λλ c) x Avogadro'sc) x Avogadro's
number = 1.54 x 10number = 1.54 x 10-4-4
J/molJ/mol

7
What is the wavelength?What is the wavelength?
Of an electron with a mass of 9.11 x 10Of an electron with a mass of 9.11 x 10-31-31
kgkg
traveling at 1.0 x 10traveling at 1.0 x 1077
m/s? Note: all em/s? Note: all e--
s haves have
same mass & 1 joule = 1 Kg msame mass & 1 joule = 1 Kg m22
/s/s22
UseUse λλ = h/mv to get . . .= h/mv to get . . .
7.27 x 107.27 x 10-11-11
m for the electronm for the electron
Of a softball with a mass of 0.10 kg moving atOf a softball with a mass of 0.10 kg moving at
125125 mi/hrmi/hr?? Same equation to get . . .Same equation to get . . .
1.9 x 101.9 x 10-34-34
m for the ball (Compare to electron)m for the ball (Compare to electron)

8
DiffractionDiffraction
When light passes through, or reflectsWhen light passes through, or reflects
off, a series of thinly spaced lines, itoff, a series of thinly spaced lines, it
creates a rainbow effect.creates a rainbow effect.
This is because the wavesThis is because the waves interfereinterfere withwith
each other.each other.
LD 1: 4.14LD 1: 4.14

3
Two Curveswith two holes
Interfere with
each other

4
Two Curveswith two holes
Interfere with
each other
crests add up

6
Several waves
Several Curves

7
Several wavesSeveral waves
Interferenc
e Pattern
Several Curves

8
What will an electron do if diffracted?What will an electron do if diffracted?
It hasIt has massmass, so it is matter., so it is matter.
AA particleparticle can only go throughcan only go through oneone hole.hole.
AA wavewave can go throughcan go through bothboth holes.holes.
AnAn electronelectron does go though both, anddoes go though both, and
makes anmakes an interference patterninterference pattern..
It behaves like a wave.It behaves like a wave.
Other matter have wavelengths tooOther matter have wavelengths too
short to notice.short to notice.

9
Figure 7.5 The Constructive andFigure 7.5 The Constructive and
Destructive Interference of WavesDestructive Interference of Waves
a.a. Diffraction occurs whenDiffraction occurs when
electromagnetic radiation iselectromagnetic radiation is
scatteredscattered from a regular arrayfrom a regular array
such as NaCl crystals.such as NaCl crystals.
b.b. Bright spotsBright spots fromfrom constructiveconstructive
interference of waves.interference of waves.
c.c. Dark areasDark areas fromfrom destructivedestructive
interference.interference.

0
SpectrumSpectrum
The range of frequencies present inThe range of frequencies present in
light.light.
White light has a continuousWhite light has a continuous
spectrum.spectrum.
All the colors are possible.All the colors are possible.
A rainbow.A rainbow.

1
A ContinuousA Continuous
Spectrum (a) andSpectrum (a) and
A Hydrogen LineA Hydrogen Line
Spectrum (b)Spectrum (b)

42
7.3 Atomic Spectrum of Hydrogen
Emission spectrum because these are the
colors it gives off or emits. LD1: 4.7
Called a line spectrum. Each element has
a unique one. Like a fingerprint.
There are just a few discrete lines showing
410 nm
434 nm
486 nm
656 nm

Line emission spectra of H, Hg, and Ne

44
What this means
Only certain energies are allowed for
the electron in an hydrogen atom.
Can only give off certain energies.
Use ∆E = hν = hc / λ
Energy in the in the atom is
quantized.
This is where we get quantum theory.

45
7.4 The Bohr Model
Niels Bohr developed the quantum model of
the hydrogen atom.
He said electrons move like planets
around the sun (later found
incomplete).
Only works for hydrogen electron & other
monoelectronic species (e.g., He1+
ion).
The electrons were attracted to the nucleus
because of opposite charges.
Did not fall in to the nucleus because they
were moving around very rapidly.

46
The Bohr Ring Atom
He didn’t know why but only certain
energies were allowed.
He called these allowed energies energy
levels.
Putting energy into the atom moved the
electron away from the nucleus.
From ground state to excited state.
When it returns to ground state it gives off
light of a certain energy.
LD 1: 4.9

47
The Bohr Ring Atom
n = 3
n = 4
n = 2
n = 1

8
The Bohr ModelThe Bohr Model
n is the energy leveln is the energy level
for each energy level the energy is:for each energy level the energy is:
E = -2.178 x 10E = -2.178 x 10-18-18
J (ZJ (Z22
/ n/ n22
))
Z is the nuclear charge, which is +1Z is the nuclear charge, which is +1
for hydrogen (+2 for Hefor hydrogen (+2 for He11
+ ion, etc.).+ ion, etc.).
n = 1 is called the ground staten = 1 is called the ground state
when the electron is removed, n = ∞when the electron is removed, n = ∞
E = 0E = 0

9
We are worried about the changeWe are worried about the change
When the electron moves from oneWhen the electron moves from one
energy level to another in an H atomenergy level to another in an H atom
(I.e., Z = 1).(I.e., Z = 1).
∆∆E = EE = Efinalfinal - E- Einitialinitial
∆∆E = -2.178 x 10E = -2.178 x 10-18-18
J ZJ Z22
(1/ n(1/ nff
22
- 1/ n- 1/ nii
22
))
Use for monoelectronic species onlyUse for monoelectronic species only
(e.g. He(e.g. He1+1+
ion)ion)

0
Examples if timeExamples if time
∆∆E = -2.178 x 10E = -2.178 x 10-18-18
J ZJ Z22
(1/ n(1/ nff
22
- 1/ n- 1/ nii
22
))
Calculate the energy needed to move a hydrogenCalculate the energy needed to move a hydrogen
electron from its first level to the third energyelectron from its first level to the third energy
level. Ans. . .level. Ans. . .
1.936 x 101.936 x 10-18-18
JoulesJoules
Calculate the E released when an electronCalculate the E released when an electron
moves from n= 4 to n=2 in a hydrogen atom.moves from n= 4 to n=2 in a hydrogen atom.
-4.084 x 10-4.084 x 10-19-19
Joules (negative value meansJoules (negative value means
energyenergy releasedreleased))
Calculate the E released when an e- moves fromCalculate the E released when an e- moves from
n= 5 to n=3 in a Hen= 5 to n=3 in a He+1+1
ionion ((monoelectronic speciesmonoelectronic species))
-6.195 x 10-6.195 x 10-19-19
Joules (negative value meansJoules (negative value means
energyenergy releasedreleased))

1
When is it true?When is it true?
OnlyOnly for hydrogen atoms and otherfor hydrogen atoms and other
monoelectronic species.monoelectronic species.
Why the negative sign?Why the negative sign?
To decrease the energy of the electronTo decrease the energy of the electron
(i.e., the system) you make it closer to(i.e., the system) you make it closer to
the nucleus.the nucleus.
the maximum energy an electron canthe maximum energy an electron can
have is zero, at an infinite distance.have is zero, at an infinite distance.

2
When is it true?When is it true?
a.a. Model correctly fits the quantitized energyModel correctly fits the quantitized energy
levels oflevels of H atomH atom and postulatesand postulates only certainonly certain
allowed circular orbitsallowed circular orbits for the electron.for the electron.
b.b. As e- becomes moreAs e- becomes more tightlytightly bound, itsbound, its
energy becomesenergy becomes more negativemore negative relative torelative to
the zero-energy reference statethe zero-energy reference state
(corresponding to the e- being at infinite(corresponding to the e- being at infinite
distance from the nucleus).distance from the nucleus). As e- is broughtAs e- is brought
closer to nucleus, energy iscloser to nucleus, energy is releasedreleased fromfrom
the system.the system.

3
Bohr’s ModelBohr’s ModelIncreasingenergy
Nucleus
First
Second
Third
Fourth
Fifth
}
Further awayFurther away
from thefrom the
nucleus meansnucleus means
more energy.more energy.
There is no “in-There is no “in-
between”between”
energyenergy
Energy LevelsEnergy Levels

54
The Bohr Model
Doesn’t work generally.
Only works for hydrogen atoms (and
other monoelectronic species).
Electrons do not move in circles.
The energy quantization is right, but
not because they are circling like
planets.
So, we need another model (LD 4.12)

5
7.5 The Quantum Mechanical Model7.5 The Quantum Mechanical Model
A totally new approach.A totally new approach.
De Broglie said matter could be like aDe Broglie said matter could be like a
wave.wave.
De Broglie said they were like standingDe Broglie said they were like standing
waves.waves.
The vibrations of a stringed instrument.The vibrations of a stringed instrument.

57
Standing Waves - fixed or “quantized”
wavelengths, d = n(λ/2)
nodes
d = (1/2) λ
d = λ
d = (3/2) λ

8
The Standing WavesThe Standing Waves
Caused by the Vibration ofCaused by the Vibration of
a Guitar String Fastened ata Guitar String Fastened at
Both Ends.Both Ends.
Each dot represents a nodeEach dot represents a node
(a point of zero(a point of zero
displacement).displacement).

59
What’s possible?
You can only have a standing wave if you
have complete waves (standing wave
generator demo).
There are only certain allowed waves.
In the atom there are certain allowed waves
called electrons.
1925 Erwin Schrödinger described the
wave function of the electron.
Much math but what is important are the
solutions.

0
The Hydrogen ElectronThe Hydrogen Electron
Visualized as a Standing WaveVisualized as a Standing Wave
Around the NucleusAround the Nucleus
Destructive interference occursDestructive interference occurs
if orbit does not equal aif orbit does not equal a
complete wave.complete wave.
So only certain electronSo only certain electron
energies are allowed.energies are allowed.

“allowed”
orbit =
constructive
interference
“forbidden”
orbit =
destructive
interference
Standing Waves
E. Schrödinger (1927)

62
The Schrodinger Wave Equation
Energy is quantized. It comes in chunks.
A quanta is the amount of energy needed to
move from one energy level to another.
Since the energy of an atom is never “in-
between” there must be a quantum leap in
energy.
Schrodinger derived an equation that
described the energy and probable position
of the electrons in an atom.

63
Schrödinger’s Equation
The wave function is a F(x, y, z)
Solutions to the equation are called
orbitals.
These are not Bohr orbits.
Each solution is tied to a certain energy.
These are the energy levels.

4
There is a limit to what we canThere is a limit to what we can
knowknow
We can’t know how the electron isWe can’t know how the electron is
moving or how it gets from one energymoving or how it gets from one energy
level to another.level to another.
The Heisenberg Uncertainty Principle.The Heisenberg Uncertainty Principle.
There is a limit to how well we can knowThere is a limit to how well we can know
both the position and the momentum ofboth the position and the momentum of
an object.an object.

65
Heisenberg Uncertainty Principle
It is impossible to know exactly the
position and velocity of a particle at
the same time.
The better we know one, the less we
know the other.
The act of measuring changes the
properties.

66
More obvious with the very small
To measure where a electron is, we use light.
But the light moves the electron
And hitting the electron changes the frequency of
the light.
Both the electron and the light are changed by the
collision.
Light photons are too small to affect anything other
than electrons in the manner.

7
Moving
Electron
Photon
Before
Electron
Changes velocity
Photon
changes
wavelength
After

8
MathematicallyMathematically
∆∆x ·x · ∆∆(mv) > h/4(mv) > h/4ππ
∆∆x is the uncertainty in the position.x is the uncertainty in the position.
∆∆(mv) is the uncertainty in the(mv) is the uncertainty in the
momentum.momentum.
the minimum uncertainty is h/4the minimum uncertainty is h/4ππ

We can never SIMULTANEOUSLY know with absolute
precision both the exact position (x), and momentum
(mass X velocity or mv), of the electron.
∆x • ∆(mv) > h
Uncertainty in
momentum
Uncertainty
in position
Planck’s
constant
If one uncertainty gets very small, then the other becomes
very large

If an electron is moving at 1.0 X 108
m/s with an uncertainty
in velocity of 0.10 %, then what is the uncertainty in
position?
∆x • ∆(mv) > h and rearranging
∆x > h / ∆(mv) or since the mass is fixed
∆x > h / m∆v
∆x > 7.3 X 10-9
m or 7300 pm
∆x > (6.63 X 10-34
Js)
(9.11 X 10-31
kg)(.001 X 1 X 108
m/s)

1
Examples - Plug & ChugExamples - Plug & Chug
We’ll skip the problems, know the conceptWe’ll skip the problems, know the concept
What is the uncertainty in the position ofWhat is the uncertainty in the position of
an electron. mass 9.31 x 10an electron. mass 9.31 x 10--3131
kg with ankg with an
uncertainty in the speed of .100 m/suncertainty in the speed of .100 m/s
What is the uncertainty in the position ofWhat is the uncertainty in the position of
a baseball, mass .145 kg with ana baseball, mass .145 kg with an
uncertainty in the speed of .100 m/suncertainty in the speed of .100 m/s

2
What does the wave Function mean?What does the wave Function mean?
Nothing.Nothing.
It is not possible to visually map it.It is not possible to visually map it.
The square of the function is theThe square of the function is the
probability of finding an electron near aprobability of finding an electron near a
particular spot.particular spot.
Best way to visualize it is by mappingBest way to visualize it is by mapping
the places where the electron is likely tothe places where the electron is likely to
be found.be found.

3
Probability
Distance from nucleus

4
SumofallProbabilitiesSumofallProbabilities
Distance from nucleusDistance from nucleus

5
Defining the sizeDefining the size
The nodal surface.The nodal surface.
The size that encloses 90% to theThe size that encloses 90% to the
total electron probability.total electron probability.
NOT at a certain distance, but a mostNOT at a certain distance, but a most
likely distance.likely distance.
For the first solution it is a sphere.For the first solution it is a sphere.

We can construct atomic orbitals by drawing a boundary at
the place where probability = 90%

77
Note on online HW pp
#6 is correct - check your units!.
When a question asks, “how much heat is
liberated,” your answer will be positive
because there is no “negative” heat.
When a question asks, “what is the
change in heat” then you have to indicate
the change by a (+) or (-) sign.
When you use energy or heat in a
mathematical equation (e.g., q = m∆TCp
then you also have to show the sign.

78
7.6 Quantum Numbers
There are many solutions to
Schrödinger’s equation
Each solution can be described with 4
quantum numbers (n, l, m, s) that
describe some aspect of the solution.
Analogous to y = mx + b describing a
line (4 variables).

79
Atomic Orbitals & Quantum Numbers
Principal Quantum Number (n) = the
main energy level of the electron.
Tells us the size (distance from the
nucleus) and energy of an orbital.
Has integer values of n = 1, 2, 3, . . .

80
Angular Momentum Quantum Number (l)
Within each energy level the complex
math of Schrodinger’s equation
describes several shapes (l).
These shapes are called atomic
orbitals
They are regions where there is a
high probability of finding an electron.

81
The 2nd quantum number
Angular momentum quantum number l .
Describes the shape of the orbital.
Has integer values from 0 to n-1
l = 0 is called s and has shape of?
l = 1 is called p
l = 2 is called d
l = 3 is called f
l = 4 is called g

82
3rd Quantum number (m)
Magnetic quantum number (ml)
Has integer values between -l and +l
Tells orientation of each shape.

+
n = 1
n = 2
n = 3
1s
2s
3s
Orbitals are found in 3-D shells
instead of 2-D Bohr orbits. The
Bohr radius for n=1 was correct,
however.

+
n = 1
n = 2
n = 3
“p” orbitals only exist in the 2nd shell and higher (n = 2, 3, ...)
3px 3py 3pz
2px 2py 2pz

“d” orbitals only exist for n = 3, 4, 5….
+
n = 1
n = 2
n = 3
3dz
2
3dxz 3dyz 3dxy 3dx2-y2

Do not appear until the 4th shell and higher

“The Shell Game”
(n = 1)
+
n = 1
n = 2
n = 3

n = 2
+
n = 1
n = 2
n = 3

n = 3
+
n = 1
n = 2
n = 3

Go to application, Atom in a BoxGo to application, Atom in a Box
pp
100

Quantum Numbers
n = # of sublevels per level
n2
= # of orbitals per level
Sublevel sets: 1 s, 3 p, 5 d, 7 f
101

102
7.8 Electron Spin & the Pauli Principle
4th Quantum number (s)
Electron spin quantum number (either
symbolized as “s” or as “ ms”)
Can have 2 values only.
Either +1/2 or -1/2
LD 1: 4.30 & 4.31 Electron Spin

03
A Picture ofA Picture of
the Spinningthe Spinning
ElectronElectron

104
Pauli Exclusion Principle
No two electrons in the same atom can
have the same set of 4 quantum
numbers. This means . . .
At most 2 electrons per orbital - each
with different spins

05
7.9 Polyelectronic Atoms7.9 Polyelectronic Atoms
More than one electron.More than one electron.
Three energy contributions.Three energy contributions.
TheThe kinetickinetic energy of moving electrons.energy of moving electrons.
TheThe potentialpotential energy of theenergy of the attractionattraction
between the nucleus and the electrons.between the nucleus and the electrons.
TheThe potentialpotential energy fromenergy from repulsionrepulsion ofof
electrons.electrons.

06
Polyelectronic atomsPolyelectronic atoms
Can’t solve Schrödinger's equation exactly.Can’t solve Schrödinger's equation exactly.
Difficulty isDifficulty is repulsionrepulsion of other electrons.of other electrons.
Solution is to treat each electron as if it wereSolution is to treat each electron as if it were
affected by theaffected by the net fieldnet field of charge from theof charge from the
attraction of the nucleus and the repulsion ofattraction of the nucleus and the repulsion of
the electrons.the electrons.
EffectiveEffective nuclear chargenuclear charge

07
+11P
11 electrons
+11P 10 other
electrons
e-Zeff

08
Effective Nuclear chargeEffective Nuclear charge
Can be calculated fromCan be calculated from
E = -2.178 x 10E = -2.178 x 10-18-18
J (ZJ (Zeffeff
22
/ n/ n22
))
andand
∆∆E = -2.178 x 10E = -2.178 x 10-18-18
J ZJ Zeffeff
22
(1/ n(1/ nff
22
- 1/ n- 1/ nii
22
))

09
Summary: Polyelectronic EffectSummary: Polyelectronic Effect
In a hydrogen atom there is only oneIn a hydrogen atom there is only one
electron.electron.
So, its energySo, its energy sublevelssublevels (orbitals) are(orbitals) are
equal (because no interference fromequal (because no interference from
other electrons).other electrons).

10
OrbitalOrbital
EnergyEnergy
Levels forLevels for
thethe
HydrogenHydrogen
AtomAtom
(degenerate)(degenerate)

11
Figure 7.18 Orbital Energy Levels for the H Atom (degenerate)Figure 7.18 Orbital Energy Levels for the H Atom (degenerate)

12
Summary continuedSummary continued
But, in a polyelectronic orbital theBut, in a polyelectronic orbital the
sublevels are not equal in energy.sublevels are not equal in energy.
Electrons “prefer” the orderElectrons “prefer” the order s, p, d, fs, p, d, f..
E.g.,E.g., the 2s electron “penetrates” to thethe 2s electron “penetrates” to the
nucleus more than the 2p enucleus more than the 2p e--
..
So, the 2s orbital is lower in energy.So, the 2s orbital is lower in energy.
Penetration effects produces thePenetration effects produces the
Aufbau principle (arrow diagram)Aufbau principle (arrow diagram)

13
Increasingenergy
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f

14
7.10 The History of the Periodic Table7.10 The History of the Periodic Table
Developed independently by GermanDeveloped independently by German
Julius Lothar Meyer and Russian DmitriJulius Lothar Meyer and Russian Dmitri
Mendeleev (1870”s).Mendeleev (1870”s).
Didn’t know much about the atom.Didn’t know much about the atom.
Put in columns by similar properties.Put in columns by similar properties.
Predicted properties of missingPredicted properties of missing
elements.elements.

115
History of the Periodic Table
Russian scientist, Dmitri Mendeleev,
taught chemistry in terms of properties.
Mid 1800 - molar masses of elements
were known.
He wrote down the elements in order of
increasing atomic mass.
He found a pattern of repeating
properties.

116
Mendeleev’s Table
Grouped elements in columns by similar
properties in order of increasing atomic
mass.
Found some inconsistencies - felt that the
properties were more important than the
mass, so switched order for some.
He found some gaps. He concluded . . .
Must be undiscovered elements.
Predicted their properties before they were
found. (Sc, Ga, Ge)

Mendeleev’s Early Periodic Table, Published in 1872
Note the spaces left for missing elements with atomic masses 44,
68, 72 and 100.
117

118
Mendeleev’s Table
Two questions remained:
Why can most elements be arranged in
order of atomic mass, but a few can’t?
What was the reason for chemical
periodicity?
Mosely: found the patterns fit better
when arranged in order of nuclear
charge (the atomic number vs. mass).

119
The modern table
The Periodic Law: physical & chemical
properties of the elements are periodic
functions of their atomic numbers.
The Periodic Table: Arranges elements in
order of increasing atomic number (not
mass), so elements with similar properties
are in the same group (column).
Let’s look at an example of this . . .

120
Modern PT by atomic # (& properties)
Compare Sb, Te, I (look at your PT)
Gp # →
(Per. 5)
15 16 17
Name Antimony Tellurium Iodine
Mass # 121.75 127.60 126.90
Symbol Sb Te I
Atomic # 51 52 53

121
The Modern Table
Elements still grouped by properties.
Similar properties in the same column.
Order is in increasing atomic number.
Added a column of elements Mendeleev
didn’t know about (noble gases).
The noble gases weren’t found because
they didn’t react with anything.
Last column on the Periodic Table
Also added lanthanides & actinides.

22
7.11 The Aufbau Principle & the Periodic Table7.11 The Aufbau Principle & the Periodic Table
Aufbau is German for building up.Aufbau is German for building up.
As the protons are added one by one,As the protons are added one by one,
the electrons fill up hydrogen-likethe electrons fill up hydrogen-like
orbitals.orbitals.
Fill up in order of energy levels.Fill up in order of energy levels.
This causes difficulties because of theThis causes difficulties because of the
overlap of orbitals of different energies.overlap of orbitals of different energies.

23
Increasingenergy
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
He with 2
electrons

24
Hund’s RuleHund’s Rule
When electrons occupy orbitals of equalWhen electrons occupy orbitals of equal
energy they doenergy they do notnot pair up until theypair up until they
have to. (Each gets its own room)have to. (Each gets its own room)
Let’s determine the electronLet’s determine the electron
configuration forconfiguration for PhosphorusPhosphorus
Need to account for 15 electrons (sameNeed to account for 15 electrons (same
as atomic number)as atomic number)

125
The first two electrons
go into the 1s orbital
Notice the opposite
spins
only 13 more to go
Increasingenergy
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f

126
The next electrons
go into the 2s orbital
only 11 more
Increasingenergy
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f

127
• The next electrons go
into the 2p orbital
• only 5 more
Increasingenergy
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f

128
• The next electrons go
into the 3s orbital
• only 3 more
Increasingenergy
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f

129
Increasingenergy
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
• The last three electrons
go into the 3p orbitals.
• They each go into
separate shapes
• 3 unpaired electrons
• 1s2
2s2
2p6
3s2
3p3

130
Orbital Diagrams
Use individual orbitals
Give subshell arrangement
Each orbital takes one electron
before any other orbital in the same
subshell can receive a second
electron

131
Orbital Diagram for A Nitrogen
Atom
N
1s 2s 2p 3s
↑↓ ↑↓ ↑ ↑ ↑

132
Orbital Diagram for A Fluorine
Atom
F
1s 2s 2p 3s
↑↓ ↑↓ ↑↑↓ ↑↓

133
Orbital Diagram for A
Magnesium Atom
Mg
1s 2s 2p 3s
↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓

134
Learning Check O1
Write the orbital diagram for the
electrons in an oxygen atom. . . Ans.

135
Solution O1
Write the orbital diagram for the electrons
in an oxygen atom.
1s 2s 2p 3s
↑↓ ↑
↓
↑↑↓ ↑

36
Tr23 Aufbau PrincipleTr23 Aufbau Principle
What is the maximum
electrons in each box?
Two
Which is a higher energy
level, 4d or 5s?
4d
Which is farther from the
nucleus, 4d or 5s?
5s

37
DetailsDetails
Valence electronsValence electrons - s & p electrons in- s & p electrons in
the outermost energy sublevels (not d).the outermost energy sublevels (not d).
Core electronsCore electrons- the inner electrons.- the inner electrons.
Hund’s RuleHund’s Rule - The lowest energy- The lowest energy
configuration for an atom is the oneconfiguration for an atom is the one
having the maximum number ofhaving the maximum number of
unpairedunpaired electrons in the orbitalelectrons in the orbital..
C 1sC 1s22
2s2s22
2p2p22

38
Fill from the bottom up followingFill from the bottom up following
the arrowsthe arrows
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
• 1s2
• 2• electrons
2s2
• 4
2p6
3s2
• 12
3p6
4s2
• 20
3d10
4p6
5s2
• 38
4d10
5p6
6s2
• 56

39
DetailsDetails
Elements in theElements in the samesame column have thecolumn have the
same outersame outer electron configurationelectron configuration..
Put in columns because ofPut in columns because of similarsimilar
propertiesproperties..
Similar propertiesSimilar properties becausebecause of electronof electron
configuration.configuration.
Noble gases haveNoble gases have filledfilled energy levels.energy levels.
Transition metals are filling theTransition metals are filling the dd orbitalsorbitals

140
Sublevel Blocks
s1
s2
p1
p2
p3
p4
p5
p6
1
2
3 d1
- d10
4
5
6
f1
- f14

141
The “Extended” Periodic Table pp

142
1s1
1s2
2s1
1s2
2s2
2p6
3s1
1s2
2s2
2p6
3s2
3p6
4s1
1s2
2s2
2p6
3s2
3p6
4s2
3d10
4p6
5s1
1s2
2s2
2p6
3s2
3p6
4s2
3d10
4p6
5s2
4d10
5p6
6s1
H
1
Li
3
Na
11
K
19
Rb
37
Cs
55
Fr
87

143
He
2
Ne
10
Ar
18
Kr
36
Xe
54
Rn
86
1s2
1s2
2s2
2p6
1s2
2s2
2p6
3s2
3p6
1s2
2s2
2p6
3s2
3p6
4s2
3d10
4p6
1s2
2s2
2p6
3s2
3p6
4s2
3d10
4p6
5s2
4d10
5p6

44
ExceptionsExceptions
Ti = [Ar] 4sTi = [Ar] 4s22
3d3d22
V = [Ar] 4sV = [Ar] 4s22
3d3d33
Cr = [Ar] 4sCr = [Ar] 4s11
3d3d55
Mn = [Ar] 4sMn = [Ar] 4s22
3d3d55
Half filled orbitals (only with d-orbitals).Half filled orbitals (only with d-orbitals).
Scientists aren’t sure of why it happens.Scientists aren’t sure of why it happens.
same for Cu [Ar] 4ssame for Cu [Ar] 4s11
3d3d1010

45
Aufbau Web GraphicAufbau Web Graphic
http://intro.chem.okstate.edu/WorkshopFohttp://intro.chem.okstate.edu/WorkshopFo

46
More exceptionsMore exceptions
Lanthanum La: [Xe] 6sLanthanum La: [Xe] 6s22
5d5d11
Cerium Ce: [Xe] 6sCerium Ce: [Xe] 6s22
4f4f11
5d5d11
Promethium Pr: [Xe] 6sPromethium Pr: [Xe] 6s22
4f4f33
5d5d00
Gadolinium Gd: [Xe] 6sGadolinium Gd: [Xe] 6s22
4f4f77
5d5d11
Lutetium Pr: [Xe] 6sLutetium Pr: [Xe] 6s22
4f4f1414
5d5d11
Then we go back to Aufbau filling:Then we go back to Aufbau filling:
Hafnium Hf: [Xe] 6sHafnium Hf: [Xe] 6s22
4f4f1414
5d5d22
We’ll just pretend that all except Cu andWe’ll just pretend that all except Cu and
Cr follow the rules.Cr follow the rules.

47
A Quick DetourA Quick Detour
The concept of shielding andThe concept of shielding and
penetration of electrons in orbitals.penetration of electrons in orbitals.
Catch the concepts, don’t worry tooCatch the concepts, don’t worry too
much about the math.much about the math.
Some AP questions.Some AP questions.
This detour includes next 18 slides.This detour includes next 18 slides.

48
More PolyelectronicMore Polyelectronic
We can use ZWe can use Zeffeff toto predict propertiespredict properties, if, if
we determine its pattern on the periodicwe determine its pattern on the periodic
table.table.
Can use the amount of energy it takesCan use the amount of energy it takes
toto removeremove an electron for this.an electron for this.
Ionization EnergyIonization Energy - The energy- The energy
necessary to remove an electron from anecessary to remove an electron from a
gaseousgaseous atom.atom.

49
Remember this?Remember this?
E = -2.18 x 10E = -2.18 x 10-18-18
J(ZJ(Z22
/n/n22
))
was true for Bohr atom.was true for Bohr atom.
Can be derived from quantum mechanicalCan be derived from quantum mechanical
model as wellmodel as well
For a mole of electrons beingFor a mole of electrons being removedremoved (so(so
use positive value for E).use positive value for E).
E =(6.02 x 10E =(6.02 x 102323
/mol)2.18 x 10/mol)2.18 x 10-18-18
J(ZJ(Z22
/n/n22
))
E = 1.31 x 10E = 1.31 x 1066
J/mol(ZJ/mol(Z22
/n/n22
))
E = 1310 kJ/mol(ZE = 1310 kJ/mol(Z22
/n/n22
))

50
ExampleExample
Calculate the ionization energy of BCalculate the ionization energy of B+4+4
E = 1310 kJ/mol(ZE = 1310 kJ/mol(Z22
/n/n22
))
1310(51310(522
)/1)/122
n= 1 because then= 1 because the remainingremaining 1s e- is1s e- is
being removed) = 32 750 kJ/molbeing removed) = 32 750 kJ/mol

51
Remember our simplified atomRemember our simplified atom
+11
11 e-
Zeff
1 e-

52
This gives usThis gives us
Ionization energy =Ionization energy =
1310 kJ/mol(Z1310 kJ/mol(Zeffeff
22
/n/n22
))
So we can measure ZSo we can measure Zeffeff
The ionization energy for a 1s electronThe ionization energy for a 1s electron
from sodium is 1.39 x 10from sodium is 1.39 x 1055
kJ/mol .kJ/mol .
The ionization energy for a 3s electronThe ionization energy for a 3s electron
from sodium is 4.95 x 10from sodium is 4.95 x 1022
kJ/mol .kJ/mol .
DemonstratesDemonstrates shielding.shielding.

153
Shielding
The electron on the
outside energy level
has to look through all
the other energy levels
to see the nucleus.

154
Shielding
So, it is less affected by
the nucleus.
So, lower effective
nuclear charge on it
(blocking by the inner
electrons)
And easier to be
removed.
So, lower IE

55
ShieldingShielding
Electrons on theElectrons on the higherhigher energy levelsenergy levels
tend to betend to be farther outfarther out..
Have to lookHave to look throughthrough the other electronsthe other electrons
to see the nucleus.to see the nucleus.
So, less affected by the nucleus.So, less affected by the nucleus.
LowerLower effectiveeffective nuclear chargenuclear charge on themon them
IfIf shielding were completely effective, Zshielding were completely effective, Zeffeff
= 1 (= 1 (e.ge.g., in Na, 10 p., in Na, 10 p++
cancel 10 ecancel 10 e--
leavingleaving
the 11th pthe 11th p++
to have a Z effect on the 11thto have a Z effect on the 11th
ee--
Why isn’t the shielding complete?Why isn’t the shielding complete?

56
PenetrationPenetration
There are levels to the electronThere are levels to the electron
distribution for each orbital.distribution for each orbital.
2s

57
GraphicallyGraphically
Penetration
2s
RadialProbability

58
GraphicallyGraphicallyRadialProbability
3s

59
RadialProbability
3p

60
RadialProbability
3d

61
RadialProbability
4s
3d

62
Penetration effectPenetration effect
The outer energy levelsThe outer energy levels penetratepenetrate thethe
inner levels so the shielding of theinner levels so the shielding of the corecore
electrons is not totally effective.electrons is not totally effective.
From most penetration to leastFrom most penetration to least
penetration the order ispenetration the order is
ns > np > nd > nf (within thens > np > nd > nf (within the samesame
energy level).energy level).
This is what gives us our order ofThis is what gives us our order of filling,filling,
electrons prefer s and p.electrons prefer s and p.

63
How orbitals differHow orbitals differ
The more positive the nucleus, theThe more positive the nucleus, the
smaller the orbital.smaller the orbital.
A sodium 1s orbital is the sameA sodium 1s orbital is the same shapeshape
as a hydrogen 1s orbital, but it isas a hydrogen 1s orbital, but it is
smallersmaller because the electron is morebecause the electron is more
strongly attracted to the nucleus (11 Pstrongly attracted to the nucleus (11 P++
vs. 1 Pvs. 1 P++
).).
The helium 1s is smaller than H’s 1sThe helium 1s is smaller than H’s 1s
also.also.
This provides for better shielding.This provides for better shielding.

65
Zeff
1
2
4
5
1
If shielding is perfect Z= 1

66
Zeff
1
2
4
5
1
Noshielding
Z=Z
eff

68
Back To Basics NowBack To Basics Now
Let’s look at periodic trends.Let’s look at periodic trends.

69
7.12 Periodic Trends in Atomic Properties7.12 Periodic Trends in Atomic Properties
Ionization energy is the energy required toIonization energy is the energy required to
removeremove an electron from aan electron from a gaseousgaseous atom.atom.
XX(g)(g) + energy+ energy →→ XX++
(g)(g) + e+ e--
HighestHighest energy electron removedenergy electron removed firstfirst..
First ionization energy (First ionization energy (II11) is that required) is that required
to remove the first electron.to remove the first electron.
Second ionization energy (Second ionization energy (II22) - the second) - the second
electronelectron
etc. etc.etc. etc.

70
Trends in ionization energyTrends in ionization energy
for Mgfor Mg
• II11 = 735 kJ/mole= 735 kJ/mole
TheThe effectiveeffective nuclear chargenuclear charge increasesincreases asas
you remove electrons.you remove electrons.
Notice the big jump between INotice the big jump between I22 and Iand I3.3.
It takes much more energy to remove aIt takes much more energy to remove a
corecore electron than a valence electronelectron than a valence electron
because there isbecause there is lessless shielding.shielding.

171
Symbol First Second Third
H
He
Li
Be
B
C
N
O
F
Ne
1312
2731
520
900
800
1086
1402
1314
1681
2080
5247
7297
1757
2430
2352
2857
3391
3375
3963
11810
14840
3569
4619
4577
5301
6045
6276

172
Symbol First Second Third
H
He
Li
Be
B
C
N
O
F
Ne
1312
2731
520
900
800
1086
1402
1314
1681
2080
5247
7297
1757
2430
2352
2857
3391
3375
3963
11810
14840
3569
4619
4577
5301
6045
6276
Why suchWhy such
increaseincrease
between thebetween the
arrows?arrows?
SpecialSpecial
stability ofstability of
noble gasnoble gas
configurationconfiguration
makes itmakes it
harder toharder to
remove anremove an
inner shellinner shell
electronelectron

173
Summary of Noble Gas Configuration effects on IE

74
Explain this trendExplain this trend
For AlFor Al
• II44 = 11,600 kJ/mole Answer . . .= 11,600 kJ/mole Answer . . .
II44 represents removing a core e-represents removing a core e-

75
Across aAcross a PeriodPeriod & Down a Group& Down a Group
Generally from left to right,Generally from left to right, II11 increasesincreases
because . . .because . . .
There is a greaterThere is a greater nuclear chargenuclear charge with thewith the
samesame shieldingshielding..
As you goAs you go downdown aa groupgroup II11 decreasesdecreases
because . . .because . . .
Electrons areElectrons are fartherfarther away.away.

76
Sample FR ProblemSample FR Problem
Given 3 different atomsGiven 3 different atoms 1s1s22
2s2s22
2p2p66
1s1s22
2s2s22
2p2p66
3s3s11
1s1s22
2s2s22
2p2p66
3s3s22
Which hasWhich has largestlargest II11? . . .? . . .
1s1s22
2s2s22
2p2p66
(Ne) - found at(Ne) - found at right end of PTright end of PT;;
also,also, 2p2p electronselectrons not effectivenot effective shieldersshielders
and the other two choices haveand the other two choices have 3s3s
electrons, which are effectively shielded byelectrons, which are effectively shielded by
thethe corecore electronselectrons and fartherand farther from thefrom the
nucleus.nucleus.

77
Sample FR ProblemSample FR Problem
Given 3 different atomsGiven 3 different atoms 1s1s22
2s2s22
2p2p66
1s1s22
2s2s22
2p2p66
3s3s11
1s1s22
2s2s22
2p2p66
3s3s22
Which hasWhich has smallestsmallest II22? . . .? . . .
1s1s22
2s2s22
2p2p66
3s3s22
(Mg) - both I(Mg) - both I11 & I& I22 involveinvolve
valence electrons (s electrons).valence electrons (s electrons).
The NaThe Na 1s1s22
2s2s22
2p2p66
3s3s11
would lose both awould lose both a
valence and a core electron from a p-valence and a core electron from a p-
orbital (hard to do).orbital (hard to do).
The NeThe Ne 1s1s22
2s2s22
2p2p66
has ineffective shieldinghas ineffective shielding
so its IE is relatively large.so its IE is relatively large.

78
It is not that simple, thoughIt is not that simple, though
ZZeffeff changeschanges as you go across a period,as you go across a period,
so willso will II11..
Half filled and filled orbitals are harderHalf filled and filled orbitals are harder
to remove electrons from.to remove electrons from.
So those have higher ISo those have higher I11 energies.energies.
Here’s what it looks like.Here’s what it looks like.

179
FirstIonizationenergy
Atomic number
He
He has a greater IE
than H because . . .
same shielding (same
level) but . . .
greater nuclear charge.
Always ask yourself
about shielding and
nuclear charge
H

180
Atomic number
H
He
Li has lower IE than H
More shielding because . . .
Further away
This outweighs greater
nuclear charge
Li

181
Atomic number
H
He
Be has higher IE than Li
same shielding (same row)
greater nuclear charge
(further away)
Li
Be

182
Atomic number
H
He
B hasB has lowerlower IE than BeIE than Be
samesame shieldingshielding (row)(row)
greatergreater nuclear chargenuclear charge butbut
By removing an electronBy removing an electron
we make s orbitalwe make s orbital filledfilled,,
which itself has lowerwhich itself has lower
energy so easier to removeenergy so easier to remove
and lower IE.and lower IE.Li
Be
B

183
Atomic number
H
He
Li
Be
B
C

184
Atomic number
H
He
Li
Be
B
C
N

185
Atomic number
H
He
Li
Be
B
C
N
O
Oxygen breaks the
pattern because
removing an
electron gets it
down to 1/2-filled p
sublevel (white
board)

186
Atomic number
H
He
Li
Be
B
C
N
O
F

187
Atomic number
H
He
Li
Be
B
C
N
O
F
Ne
Ne has a lower IE
than He. Why?. . .
Both are full, but…
Ne has more
shielding because
Greater distance
Always compare
shielding to
distance.

188
Atomic number
H
He
Li
Be
B
C
N
O
F
Ne
Na has a lower IE
than Li. Why?
Both are s1
but
Na has more
shielding because
Greater distance
(4th level)
Na

189
Atomic number

190
Tr22A Summary of the previous trends

91
The Values of First Ionization Energy for the Elements in the First Six PeriodsThe Values of First Ionization Energy for the Elements in the First Six Periods

92
Trends in Ionization Energies for theTrends in Ionization Energies for the RepresentativeRepresentative ElementsElements

193
Electron Affinity
The energy change associated with
adding an electron to a gaseous atom
Opposite to IE (which is energy for
losing an electron. A + energy → A+
+ e-
)
Has negative value (since energy is lost)
A + e-
→ A-
+ energy
Easiest to add e-
s to group 17 (why?).
Gets to full energy level (noble gas).
LD 1: 5.32 Electron affinity of Chlorine

194
Electron Affinity Trends
Period (row) Trends
Increases from left to right because atoms get
smaller, with greater nuclear charge.
Group (column) Trends
Decreases as we go down a group (i.e.,
harder to add an e-
(shielding from nucleus)
Adding electrons to (-) ions
Always more difficult to add another e-
to an
already (-) charged ion, so these affinities
have (+) values.

195
Electron Affinity Trends
Adding electrons to negative ions
Always more difficult to add another e-
to an
already (-) charged ion, so these affinities
have (+) values.

196
Table 5.17 p. 147
Observe period and group trends

197
Atomic Size
First problem: Where do you start
measuring.
The electron cloud does not have a
definite edge.
We get around this by measuring more
than 1 atom at a time as follows . . .

198
Atomic Size
Atomic Radius = half the distance between two
nuclei of a diatomic molecule
LD 1:5.22 Radius of Chlorine.
}
Radius

199
Trends in Atomic Size
Influenced by two factors:
Energy Level . . .
Higher energy level is further away.
Charge on the nucleus
More charge pulls electrons in
closer.
These are competing factors.

200
Periodic Trends
Going across a period the radius gets
smaller because . . .
Same energy level (same distance from
nucleus), but . . .
More nuclear charge.
So, outermost electrons are closer.
Na Mg Al Si P S Cl Ar

201
Group trends
As we go down a
group
Each atom has
another energy
level
So the atoms get
bigger (with some
exceptions).
H
Li
Na
K
Rb

Atomic Radii for Selected Atoms
Why is Ga smaller than Al?
Gallium, unlike Al, is preceded by
10 d-block elements
The expected increase in radius
caused by filling the 4th level is
outweighed by a shrinking of
electron cloud caused by Ga’s
nuclear charge that is
considerably larger (31 vs. 13)
than for Al.
Compare Ga & Al on next slide
(showing d-block)

Tr 26 Fig. 5.13 p. 141 Atomic Radii
Mg to Al size gets smaller because same level with more p+
s
Zn to Ga size jumps because of electron shielding from the d-
electrons that makes the increasing nuclear charge less
effective, so the electron cloud gets larger.203

204
Overall
Atomic Number
AtomicRadius(nm)
H
Li
Ne
Ar
10
Na
K
Kr
Rb

205
Tr21A Fig 5.14 p 142 Atomic Radius vs Atomic Number
How does “effective” nuclear charge change left to right
Increases
Why is there a “peak” in Period 4?
Inner 3d sublevel has filled & now in outer 4p sublevel
Why is there a U-shape curve across Period 5?
As add more 4d electrons, the shielding effect overcomes the
effective nuclear charge.

06
Parts of the Periodic TableParts of the Periodic Table

07
The information it hidesThe information it hides
Know the special groups.Know the special groups.
It is theIt is the numbernumber andand typetype of valence electronsof valence electrons
that determine an atom’sthat determine an atom’s chemistrychemistry..
You can get the electron configuration fromYou can get the electron configuration from
the periodic table.the periodic table.
MetalsMetals loselose electrons and have theelectrons and have the lowestlowest IEIE
Nonmetals -Nonmetals - gaingain electrons and have theelectrons and have the
most negativemost negative electron affinities.electron affinities.

08
The Properties of a Group: The Alkali MetalsThe Properties of a Group: The Alkali Metals
Doesn’t include hydrogen - behaves asDoesn’t include hydrogen - behaves as
a nonmetal. Going down, get:a nonmetal. Going down, get:
Decrease in IEDecrease in IE
increase in radiusincrease in radius
Decrease in densityDecrease in density
decrease in melting pointdecrease in melting point
Behave as reducing agentsBehave as reducing agents

09
Reducing abilityReducing ability
Lower IE = better reducing agents.Lower IE = better reducing agents.
Cs > Rb > K > Na > Li in reducing abilityCs > Rb > K > Na > Li in reducing ability
Works forWorks for solidssolids, but, but notnot in aqueousin aqueous
solutions. Get opposite effect.solutions. Get opposite effect.
In solution Li > K > NaIn solution Li > K > Na
Why?Why?
It’s the water - there is an energyIt’s the water - there is an energy
change associated with dissolving.change associated with dissolving.

10
Hydration EnergyHydration Energy
It is exothermicIt is exothermic
for Lifor Li++
== -510 kJ/mol-510 kJ/mol
for Nafor Na++
for Kfor K++
Li’s is so big because it has a high chargeLi’s is so big because it has a high charge
density; i.e., a lot of charge on a small atom.density; i.e., a lot of charge on a small atom.
Li loses its electron more easily because ofLi loses its electron more easily because of
this in aqueous solutionsthis in aqueous solutions

11
The reaction with waterThe reaction with water
Na and K react explosively with water.Na and K react explosively with water.
Li doesn’t.Li doesn’t. LD 1: 5.8, 5.10, 5.11, braniacsLD 1: 5.8, 5.10, 5.11, braniacs
Even though Li’s reaction has a moreEven though Li’s reaction has a more
negativenegative ∆∆H than that of Na and K.H than that of Na and K.
Na and K melt.Na and K melt.
∆∆H does not tell you speed of reactionH does not tell you speed of reaction
More about that in Chapter 12.More about that in Chapter 12.

212
Periodic (row) Trend
Metals are at the left end.
They let their electrons go easily
So, have low electronegativity
At the right end are the nonmetals.
They want more electrons.
Try to take them away from their
playmates.
So, have high electronegativity.

213
Group (column) Trend
The further down a group the farther the
electron is away and the more electrons
an atom has (and more shielding).
More willing to share with another since
the nucleus doesn’t hold on to the outer
electrons so tightly (shielding).
So, low electronegativity.

214
Ionization energy, Electronegativity,
Electron affinity INCREASE

15
Ionization energy, ElectronegativityIonization energy, Electronegativity
Electron affinity INCREASEElectron affinity INCREASE

216
Atomic size increases, (shielding
constant across a period)
Ionic size increases

17
Atomic size increases, (shieldingAtomic size increases, (shielding
constant across a period)constant across a period)
Ionic size increases

218
The Big Review
Given 5 elements
E: 2s2
2p5
G: 4d10
5s2
5p5
J: 2s2
2p2
L: 5d10
6s2
6p5
M: 2s2
2p4
ID block location (without PT).
All are in p-block
Which in same period?
EJM same period (2nd)
Same group?
EGL same group (17)

219
The Big Review
Given 5 elements
E: 2s2
2p5
G: 4d10
5s2
5p5
J: 2s2
2p2
L:
5d10
6s2
6p5
M: 2s2
2p4
Which has highest e-
affinity?
E
Forms 1-
ion?
EGL form 1 minus ions.
Highest electronegativity?
E (closest to upper right of PT)

220
The Big Review
Given 5 elements
E: 2s2
2p5
G: 4d10
5s2
5p5
J: 2s2
2p2
L:
5d10
6s2
6p5
M: 2s2
2p4
Which is larger, G or G ion?
G ion (-). Added electron, cloud is
bigger
Which contain(s) 7 valence e-
?
EGL (all have s2
p5
outer electrons)

Atomic Structure and the Quantum Model

Atomic Structure and the Quantum Model

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