Chapter 7 Atomic Structure and Periodicity 7.1 Electromagnetic Radiation electromagnetic radiation:...

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Transcript of Chapter 7 Atomic Structure and Periodicity 7.1 Electromagnetic Radiation electromagnetic radiation:...
Chapter 7Chapter 7 Atomic Structure Atomic Structure
and Periodicityand Periodicity
7.1 Electromagnetic 7.1 Electromagnetic RadiationRadiation
electromagnetic radiationelectromagnetic radiation: : form of energy that acts as a form of energy that acts as a
wave as it travelswave as it travels includes: visible light, X rays, includes: visible light, X rays,
ultraviolet and infrared light, ultraviolet and infrared light, microwaves, and radio wavesmicrowaves, and radio waves
travel at a speed of 2.9979 x 10travel at a speed of 2.9979 x 1088 m/s in a vacuumm/s in a vacuum
All forms are combined to form All forms are combined to form electromagnetic spectrumelectromagnetic spectrum
Electromagnetic Electromagnetic SpectrumSpectrum
The Wavelike ElectronThe Wavelike Electron
Louis deBroglie
The electron propagates through space as an energy
wave. To understand the atom, one must
understand the behavior of
electromagnetic waves.
Electromagnic Electromagnic radiation radiation propagates propagates through through space as a space as a wave moving wave moving at the speed at the speed of light.of light.
Wave nature of electromagnetic Wave nature of electromagnetic RadiationRadiation
wavelengthwavelength:: λλ = Greek letter lambda= Greek letter lambda distance between points on distance between points on
adjacent waves (consicutive peaks adjacent waves (consicutive peaks or troughs)or troughs)
in nm (10in nm (1099nm = 1m)nm = 1m) frequencyfrequency: :
= Greek letter nu= Greek letter nu number of wave cycles that passes number of wave cycles that passes
a point in a second. 10a point in a second. 1088 cycles/s= cycles/s= 101088 ss1 1
==101088 Hertz = 10 Hertz = 1088 Hz Hz in 1/second (Hertz = Hz)in 1/second (Hertz = Hz)
C = speed of light, a constant (3.00 x 108 m/s)
= frequency, in units of hertz (hz, sec1)
= wavelength, in meters
c
c
Long Wavelength
= Low Frequency
= Low ENERGY
Short Wavelength
= High Frequency
= High ENERGY
Wavelength TableWavelength Table
Calculate the energy of red light vs. blue light.red light: 700 nm blue light: 400 nm
hc E
red:
hc E
hc Eblue:
m10x700
)s/m10x00.3)(sJ10x62.6( E
9
834
E = 2.85 x 1019 J
m10x400
)s/m10x00.3)(sJ10x62.6( E
9
834
E = 4.96 x 1019 J
sunburn????? uv
7.27.2 Nature of MatterNature of Matter
Before 1900, scientists thought Before 1900, scientists thought that matter and energy were that matter and energy were totally differenttotally different
mattermatter energyenergyparticleparticless
massmass
positiopositionn
wavewave
masslessmassless
delocalizdelocalizeded
In 1900In 1900
Matter and energy were seen as Matter and energy were seen as different from each other in different from each other in fundamental waysfundamental ways..
Matter was particlesMatter was particles.. Energy could come in waves, with Energy could come in waves, with
any frequencyany frequency.. Max Planck found that as the Max Planck found that as the
cooling of hot objects couldn’t be cooling of hot objects couldn’t be explained by viewing energy as a explained by viewing energy as a wavewave..
e
Photoelectric effect:
Light of the right frequency (energy) can strike a metal and cause an electron to be ejected (n = infinity).
Metal surface
Nature of MatterNature of Matter
Max Planck: a German physicistMax Planck: a German physicist suggested that an suggested that an object emitsobject emits
energy in the form of small packets energy in the form of small packets of energy called of energy called quanta
QuantumQuantum the minimum amount of  the minimum amount of energy that can be gained or lost by energy that can be gained or lost by an atoman atom
Planck’s constant (h): 6.626 x 10Planck’s constant (h): 6.626 x 103434 J*sJ*s
hE
Nature of MatterNature of Matter
Einstein proposed that radiation Einstein proposed that radiation itself is really a stream of itself is really a stream of particles called particles called photonsphotons
Energy of each photon is :Energy of each photon is :
also showed that energy also showed that energy
has masshas mass
hc
hvEphoton
2mcE
Nature of MatterNature of Matter
hvE
vc c
v
hc
E
2mcE 2mc
hc
vm
h
shows that anything with both mass and velocity has a corresponding wavelength
Nature of MatterNature of Matter
In 1924, Louis de In 1924, Louis de Broglie Broglie
(French scientist)(French scientist) suggested that suggested that
matter has both matter has both particlelike and particlelike and wavelike wavelike characteristicscharacteristics vm
h
Main IdeasMain Ideas:: matter and energy are not distinctmatter and energy are not distinct energy is a form of matterenergy is a form of matter larger objects are mostly particlelikelarger objects are mostly particlelike smaller objects are mostly wavelikesmaller objects are mostly wavelike
…produces all of the colors in a continuous spectrum
Spectroscopic analysis of the Spectroscopic analysis of the visible spectrum…visible spectrum…
7.3 The Atomic Spectrum of Hydrogen7.3 The Atomic Spectrum of Hydrogen
White light
Continuous SpectraContinuous Spectra
White light passed through a prism produces a spectrum – colors in continuous form.
The Continuous The Continuous SpectrumSpectrum
The different colors of light correspond to different wavelengths and frequencies
~ 650 nm ~ 575 nm
~ 500 nm
~ 480 nm
~ 450 nm
Continuous Emission SpectrumContinuous Emission Spectrum lineemission spectrumlineemission spectrum series of series of
wavelengths of light created when wavelengths of light created when visible portion of light from excited visible portion of light from excited atoms is shined through a prismatoms is shined through a prism
scientists using classical theory scientists using classical theory expected atoms to be excited by expected atoms to be excited by whatever energy they absorbedwhatever energy they absorbed
continuous spectrumcontinuous spectrum emission of continuous range of emission of continuous range of
frequencies of EM radiationfrequencies of EM radiation contains all wavelengths of visible contains all wavelengths of visible
lightlight
…produces a “bright line” spectrum
Spectroscopic analysis of Spectroscopic analysis of the hydrogen spectrum…the hydrogen spectrum…
H receives a high energyspark
HH bondsAre broken and H atoms are excited
Line SpectraLine Spectra
Light passed through a prism from an element produces a discontinuous spectrum of specific colors
Hydrogen
only four lines are observed
Line SpectraLine Spectra
The pattern of lines emitted by excited atoms of an element is unique
= atomic emission spectrum
• These are called the atomic emission spectrum
• Unique to each element, like fingerprints!
• Very useful for identifying elements
H LineEmission H LineEmission SpectrumSpectrum
light is emitted by light is emitted by excited Hexcited H atoms when bond is broken atoms when bond is broken in thein the
diatomic moleculediatomic molecule ground stateground state lowest energy lowest energy
state of an atomstate of an atom excited stateexcited state when an atom when an atom
has higher potential energy has higher potential energy than it has at ground statethan it has at ground state
H LineEmission H LineEmission SpectrumSpectrum
when an excited electron falls when an excited electron falls back to ground state, it emits back to ground state, it emits photon of radiationphoton of radiation
the photon is equal to the the photon is equal to the difference in energy of the difference in energy of the original and final states of original and final states of electronelectron
since only certain frequencies are since only certain frequencies are emitted, only certain energies are emitted, only certain energies are allowed for electrons in H atomallowed for electrons in H atom
This produces bands of light with definite wavelengths.
Electron Electron transitionstransitionsinvolve involve jumps of jumps of definite definite amounts ofamounts ofenergy.energy.
7.47.4 The Bohr ModelThe Bohr Model Niels Bohr (Danish physicist) in 1913Niels Bohr (Danish physicist) in 1913 Developed a quantum modelDeveloped a quantum model
for H atom that explained the emission for H atom that explained the emission line spectrumline spectrum
Electron moves around the nucleus Electron moves around the nucleus only in certain allowed circular only in certain allowed circular orbitsorbits, , in which it has a certain amount of in which it has a certain amount of energyenergy
The Bohr modelThe Bohr model Energy levelEnergy level of an electron analogous of an electron analogous
to the steps of a ladderto the steps of a ladder The electron cannot exist between The electron cannot exist between
energy levels, just like you can’t stand energy levels, just like you can’t stand between steps on a ladderbetween steps on a ladder
AA quantumquantum of energy is the amount of of energy is the amount of energy required to move an electron energy required to move an electron from one energy level to anotherfrom one energy level to another
Niels BohrNiels Bohr
Developed the quantum model of the Developed the quantum model of the hydrogen atomhydrogen atom..
He said the atom was like a solar He said the atom was like a solar systemsystem..
The electrons were attracted to the The electrons were attracted to the nucleus because of opposite chargesnucleus because of opposite charges..
Didn’t fall in to the nucleus because it Didn’t fall in to the nucleus because it was moving aroundwas moving around..
The Bohr AtomThe Bohr Atom
He didn’t know why but only certain He didn’t know why but only certain energies were allowedenergies were allowed..
He called these allowed energies He called these allowed energies energy levelsenergy levels..
Putting Energy into the atom moved the Putting Energy into the atom moved the electron away from the nucleuselectron away from the nucleus..
From From ground stateground state to to excited stateexcited state.. When it returns to ground state it gives When it returns to ground state it gives
off light of a certain energyoff light of a certain energy..
The Model: SummaryThe Model: Summary Space around nucleus is divided Space around nucleus is divided
into spherical (circualr) paths into spherical (circualr) paths (orbits) each has a number called (orbits) each has a number called “Principal Quantum number”“Principal Quantum number”
The electron can exist only in one The electron can exist only in one of these orbitals but not in betweenof these orbitals but not in between
Orbits possess fixed size and Orbits possess fixed size and energy, therefore electron has a energy, therefore electron has a definite energy characteristic of its definite energy characteristic of its orbitorbit
particle
J2.180x10 constant Rydberg R
electron of
18
H
2
2
Energyn
ZREE H
orbitn
Orbits allowed for electron are Orbits allowed for electron are those in which electron has an those in which electron has an angular momentum=angular momentum=
An electron can pass only from An electron can pass only from one bit to another. Absorption or one bit to another. Absorption or emission will occuremission will occur
Energy of the outermost orbit is Energy of the outermost orbit is zero zero
molkJJ
kJX
mol
particlesXX
particle
JXEn /1312
1000
1
1
1002.610180.2
23
18
1nh
molen
kJEn
2
1312
The Bohr AtomThe Bohr Atom
n = 3n = 4
n = 2n = 1
Bohr ModelBohr Model To create an accurate model, he had to use To create an accurate model, he had to use
quantum theory instead of classicalquantum theory instead of classical created an equation used to calculate the energy created an equation used to calculate the energy
levels available to electrons in a certain atom:levels available to electrons in a certain atom:
where n= integer and Z=atomic numberwhere n= integer and Z=atomic number
negative sign makes the energy more negative the negative sign makes the energy more negative the closer it is to the nucleuscloser it is to the nucleus
)(10178.22
218
n
ZJE
Bohr ModelBohr Model
Can gain Can gain energy by energy by moving to a moving to a higher energy higher energy levellevel
Can lose Can lose energy by energy by moving to moving to lower energy lower energy levellevel
Bohr ModelBohr Model
a photon is a photon is released that released that has an energy has an energy equal to the equal to the difference difference between the between the initial and initial and final energy final energy orbitsorbits
Bohr ModelBohr Model
equation can be used twice to equation can be used twice to find the ∆E when an electron find the ∆E when an electron moves energy levelsmoves energy levels
)(10178.22
218
n
ZJE
)](10178.2[)](10178.2[ 2
218
2
2
18
i
i
f
f
n
ZJ
n
ZJE
)11
(10178.2 2218
if nnJE
Bohr ModelBohr Model can wavelength of photon released can wavelength of photon released
by using by using
E=0 is set at an distance of ∞ away E=0 is set at an distance of ∞ away from the nucleus and becomes from the nucleus and becomes more negative as the electron more negative as the electron comes closer to the nucleuscomes closer to the nucleus
E
hc
0)1
(10178.2 18
JE
Example 1Example 1
Calculate the Calculate the energy required energy required to move the to move the hydrogen hydrogen electron from electron from n=1 to n=2. n=1 to n=2. Find the Find the wavelength of wavelength of radiation that radiation that had to be had to be absorbed by the absorbed by the electronelectron..
)11
(10178.2 2218
if nnJE
JJE 1822
18 10633.1)1
1
2
1(10178.2
Jsm
sJ
E
hc18
34
10633.1
)9979.2)(10626.6(
nmm
nmm 6.121
1
1010216.1
97
Example 2Example 2Calculate the Calculate the energy energy required to required to remove the remove the electron from electron from the hydrogen the hydrogen atom in its atom in its ground stateground state..
)11
(10178.2 2218
if nnJE
)1
11(10178.2
218
JE
JJE 1818 10178.2)10(10178.2 Energy was absorbed by the electron so the value of ∆E value is positive.
The Bohr ModelThe Bohr Model
Doesn’t workDoesn’t work.. Only works for hydrogen atomsOnly works for hydrogen atoms.. Electrons don’t move in circlesElectrons don’t move in circles.. The quantization of energy is right, but The quantization of energy is right, but
not because they are circling like not because they are circling like planetsplanets..
Bohr ModelBohr Model
problems:problems: did not work for other atomsdid not work for other atoms did not explain chemical did not explain chemical
behavior of atomsbehavior of atoms
Heisenberg’s Uncertainty PrincipleHeisenberg’s Uncertainty Principle
According to de Broglie: Electron According to de Broglie: Electron behaves like a wavebehaves like a wave
It is possible to specify the position of a It is possible to specify the position of a wave at a particular instant?wave at a particular instant?
Energy, wavelength and amplitude can be Energy, wavelength and amplitude can be determined determined
But exact position is impossible to be But exact position is impossible to be determineddetermined
The electron cannot be imagined as : The electron cannot be imagined as : moving particle moving particle In a path of the same radius (well defined In a path of the same radius (well defined
orbits)orbits) Thus, location, direction and speed of Thus, location, direction and speed of
motion of a particle cannot be motion of a particle cannot be determineddetermined
Then Bohr Model had to be “Abandoned Then Bohr Model had to be “Abandoned
Heissenberg Uncertainty Heissenberg Uncertainty PrinciplePrinciple
““It is impossible to determine both It is impossible to determine both the position and momentum of a the position and momentum of a subatomic particle (such as the subatomic particle (such as the electron) with arbitrarily high electron) with arbitrarily high accuracy”accuracy” The effect of this principle is to The effect of this principle is to
convert the laws of physics into convert the laws of physics into statements about relative, instead statements about relative, instead of absolute, certainties.of absolute, certainties.
Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple
we cannot know we cannot know the exact the exact position and position and momentum momentum (motion) of the (motion) of the electronelectron
as more is known as more is known about position, about position, less is known less is known about momentumabout momentum
uncertainties are uncertainties are inversely inversely proportionalproportional
4)(
hmx
where
∆x: uncertainty in position
∆m : uncertainty in mometum
minimum minimum uncertainty uncertainty is h/4is h/4
7.57.5 The Quantum Mechanical The Quantum Mechanical ModelModel
Exactt position of electron can Exactt position of electron can not be definednot be defined Exact bath of electron about Exact bath of electron about
nucleus can not be defined nucleus can not be defined Werner HeisenbergWerner Heisenberg, , Louis de Louis de
BroglieBroglie and and Erwin SchrodingerErwin Schrodinger made the approach called made the approach called “Quantum Mechanics“Quantum Mechanics””
They assumed that the electron They assumed that the electron is a standing waveis a standing wave
The Quantum Mechanical The Quantum Mechanical ModelModel
Waves are associated with electronsWaves are associated with electrons Information about energies of Information about energies of
electrons and their positions are electrons and their positions are obtained from studying the obtained from studying the associated wavesassociated waves
Description of electron is based uponDescription of electron is based upon
“ “ Probability of finding a particle Probability of finding a particle within a given region of spacewithin a given region of space” “ ” “ but but not on the exact position” not on the exact position”
Schrödinger EquationSchrödinger Equation Wave equation describing electron Wave equation describing electron
as being a waveas being a wave The amplitudes (height),The amplitudes (height), , of , of
electron wave at various points of electron wave at various points of space are calculatedspace are calculated
commonly called “wave function”commonly called “wave function” provides information about the provides information about the
allowable energies for an electron in allowable energies for an electron in H atom. H atom.
corresponds to a certain energy corresponds to a certain energy and describes a region around and describes a region around nucleus “Orbital” where the electron nucleus “Orbital” where the electron having that energy may be foundhaving that energy may be found
Orbital:Orbital: Region around the nucleus where Region around the nucleus where the electron can be expected to be foundthe electron can be expected to be found
The Function The Function 22
22 describes the describes the probability of the probability of the position of the electron at a particular position of the electron at a particular pointpoint
22 Probablity of finding a particle in a Probablity of finding a particle in a given region of spacegiven region of space
22 Electric charge density at a given Electric charge density at a given region of spaceregion of space
ThusThus,,
The charge can be assumed to be The charge can be assumed to be spread out as a charge cloud by spread out as a charge cloud by rapid motion of electronrapid motion of electron
The cloud is denser in some The cloud is denser in some regions than othersregions than others
The probability of finding electron The probability of finding electron in a given region in space is in a given region in space is proportional to the density of the proportional to the density of the cloudcloud
Meaning of Wave Meaning of Wave FunctionFunction
the wave function itself does not the wave function itself does not have concrete meaninghave concrete meaning
the square of the wave function the square of the wave function represents the probability of represents the probability of finding an electron at a certain finding an electron at a certain pointpoint
easily represented as probability easily represented as probability distribution where the deepness distribution where the deepness of color indicates the probabilityof color indicates the probability
Meaning of Wave Meaning of Wave FunctionFunction
(a) electron density (a) electron density mapmap
probability of finding probability of finding an electron is highest an electron is highest at short distances from at short distances from nucleusnucleus
(b) calculated (b) calculated probability of finding probability of finding an electron at certain an electron at certain distances from nucleus distances from nucleus in the 1s orbitalin the 1s orbital
7.6 Quantum Numbers7.6 Quantum Numbers
There are many solutions to There are many solutions to Schroedinger’s equation for H atomSchroedinger’s equation for H atom
Each solution is a wave function Each solution is a wave function calledcalled Orbital. .
Each solution can be described with Each solution can be described with quantum numbersquantum numbers that describe that describe some aspect of the solutionsome aspect of the solution..
Schrödinger’s equation requires 3 quantum numbers
7.6 Quantum Numbers7.6 Quantum Numbers
Quantum numbers specify the Quantum numbers specify the properties of atomic orbitals and of properties of atomic orbitals and of electrons in orbitalselectrons in orbitals
the first three numbers come from the first three numbers come from the Schrödinger equation and the Schrödinger equation and describe:describe: main energy levelmain energy level shapeshape orientationorientation
44thth describes state of electron describes state of electron
11stst Quantum Number Quantum NumberPrincipal Quantum Number: Principal Quantum Number: nn Main energy level (or shell) occupied Main energy level (or shell) occupied
by electron. They are called atomic by electron. They are called atomic orbitalsorbitals regions where there is a high probability of
finding an electron.
values are all positive integers values are all positive integers >0>0 (1,2,3,…)(1,2,3,…)
As n increases size of orbital is largersize of orbital is larger electron has higher energyelectron has higher energy the electron’s average distance from the the electron’s average distance from the
nucleus increasesnucleus increases
Principal Quantum Principal Quantum NumberNumber
Maximum number of electrons that can fit in an energy level:
2n2
11stst Quantum Number Quantum Number
Energy
22ndnd Quantum Number Quantum Number
Angular Momentum Quantum Angular Momentum Quantum Number: Number: ll
indicates the indicates the shape of the orbitalshape of the orbital (sublevel or subshell)(sublevel or subshell)
the number of possible shapes (or the number of possible shapes (or ll values) for an energy level is equal to values) for an energy level is equal to nn
the possible values of the possible values of ll are 0 and all are 0 and all positive integers less than or equal to positive integers less than or equal to n n  1 1
ll has integer values from 0 to n1 has integer values from 0 to n1 ll = = 0 is called s0 is called s ll = = 1 is called p1 is called p ll = =2 is called d2 is called d ll = =3 is called f3 is called f ll = =4 is called g4 is called g
22ndnd Quantum Number Quantum Number
s orbitalss orbitals: 1: s: 1: s spherical spherical ll value of 0 value of 0 11stst occur at occur at
n=1n=1
22ndnd Quantum Quantum NumberNumber
p orbitals: 3p orbitals: 3
2p2pxx, , 2p2pyy, , 2p2pzz
dumbbelldumbbellshapedshaped
ll value of value of 11
11stst occur occur at n=2at n=2
for n>2, for n>2, shape is shape is same but same but size size increasesincreases
22ndnd Quantum Number Quantum Number
d orbitals: 5: d orbitals: 5: 3d3dxzxz, , 3d3dyzyz, , 3d3dxyxy, , 3d3dx2y2x2y2, , ddz2z2
mostly cloverleafmostly cloverleaf ll value of 2 value of 2 11stst occur at n=3 occur at n=3 for n>3, same shape but larger sizefor n>3, same shape but larger size
22ndnd Quantum Number Quantum Number
f orbitals: 7 typesf orbitals: 7 typesvarious shapesvarious shapesll value of 3 value of 3begin in n=4begin in n=4
22ndnd Quantum Number Quantum Number
Other shapes can exist in energy Other shapes can exist in energy levels as long as they follow the levels as long as they follow the rulesrules
g (l=4) starts in 5 with 9 orbitalsg (l=4) starts in 5 with 9 orbitals h (l=5) starts in 6 with 11 h (l=5) starts in 6 with 11
orbitals, etcorbitals, etc but no known elements have but no known elements have
electrons in them at ground stateelectrons in them at ground state
22ndnd Quantum Number Quantum Number
Level Sublevels Sublevels
0 1 2 3
0 1 2
0 1
0
33rdrd Quantum Number Quantum NumberMagnetic Quantum Number: Magnetic Quantum Number: mmll
indicates the orientation of an orbital indicates the orientation of an orbital around the nucleusaround the nucleus
has values from has values from ++ll  ll specifies the specifies the exact orbital that the exact orbital that the
electron is contained inelectron is contained in each orbital holds maximum of each orbital holds maximum of 2
electrons total number of orbitals is equal to total number of orbitals is equal to nn22 for for
an energy level an energy level
number of possible number of possible mmll values for a values for a
certain subshell is equal to certain subshell is equal to 22ll + 1 + 1
33rdrd Quantum Number Quantum Number
Energy Energy LevelLevel
))nn((
Sublevels Sublevels in Levelin Level
# #Orbitals Orbitals in in
SublevelSublevel
Total # Total # of of
Orbitals Orbitals in Levelin Level
11 ss 11 11
22 ss 11 44
pp 33
33 ss 11 99
pp 33
dd 55
44 ss 11 1616
pp 33
dd 55
ff 77
44thth Quantum Number Quantum Number
Spin Quantum Number: Spin Quantum Number: mmss
indicates the spin state of the indicates the spin state of the electronelectron
only 2 possible directionsonly 2 possible directions only 2 possible values: +½ and ½only 2 possible values: +½ and ½ paired electrons must paired electrons must
have opposite spinshave opposite spins maximum number of maximum number of
electrons in an energy electrons in an energy level is 2nlevel is 2n22
7.9 Polyelectronic Atoms7.9 Polyelectronic Atoms
Kinetic energy  as the Kinetic energy  as the electrons move around the electrons move around the nucleusnucleus
Potential energy  from their Potential energy  from their attraction to nucleusattraction to nucleus
Potential energy  from their Potential energy  from their repulsion to each otherrepulsion to each other
Electron Correlation ProblemElectron Correlation Problem
can’t find the exact location of can’t find the exact location of electronselectrons
can’t find the specific repulsions can’t find the specific repulsions between electronsbetween electrons
so we must treat each electron as so we must treat each electron as if it has an average amount of if it has an average amount of attraction to nucleus and attraction to nucleus and repulsion to other electronsrepulsion to other electrons
Electron ShieldingElectron Shielding
occurs when an electron is not occurs when an electron is not attracted to the nucleusattracted to the nucleus
because of electrons in lower energy because of electrons in lower energy levels repelling it.levels repelling it.
Penetration EffectPenetration Effect
all orbitals in the same energy level all orbitals in the same energy level do do NOTNOT have the same amount of have the same amount of energy ( are not degenerate)energy ( are not degenerate)
EEss < E < Epp < E < Edd < E < Eff
the amount of energy in each the amount of energy in each sublevel is determined by its sublevel is determined by its average distance from the nucleusaverage distance from the nucleus
Section 5.2Section 5.2Electron Arrangement in Electron Arrangement in
AtomsAtoms OBJECTIVES:OBJECTIVES:
• ExplainExplain why the actual why the actual electron configurations for electron configurations for some elements some elements differdiffer from from those predicted by the aufbau those predicted by the aufbau principle.principle.
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
aufbau diagram  page 133
Electron Configurations… …are the way electrons are arranged
in various orbitals around the nuclei of atoms. Three rules tell us how:
1) Aufbau principle  electrons enter the lowest energy first.
• This causes difficulties because of the overlap of orbitals of different energies – follow the diagram!
2) Pauli Exclusion Principle  at most 2 electrons per orbital  different spins
Pauli Exclusion Principle
No two electrons in an atom can have the same four quantum numbers.
Wolfgang Pauli
To show the different direction of spin, a pair in the same orbital is written as:
Quantum Numbers
Each electron in an atom has a unique set of 4 quantum numbers which describe it.
1) Principal quantum number2) Angular momentum quantum number3) Magnetic quantum number4) Spin quantum number
Electron Configurations
3) Hund’s Rule When electrons occupy orbitals of equal energy, they don’t pair up until they have to.
Let’s write the electron configuration for Phosphorus
We need to account for all 15 electrons in phosphorus
The first two electrons go into the 1s orbital
Notice the opposite direction of the spins
only 13 more to go...
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
The next electrons go into the 2s orbital
only 11 more...Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
• The next electrons go into the 2p orbital
• only 5 more...Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
• The next electrons go into the 3s orbital
• only 3 more...Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
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 (Hund’s)
• 3 unpaired electrons
• = 1s22s22p63s23p3
Orbitals fill in an order Lowest energy to higher energy.Adding electrons can change the
energy of the orbital. Full orbitals are the absolute best situation.
However, half filled orbitals have a lower energy, and are next best• Makes them more stable.• Changes the filling order
Write the electron configurations for these elements:
Titanium  22 electrons1s22s22p63s23p64s23d2
Vanadium  23 electrons1s22s22p63s23p64s23d3
Chromium  24 electrons1s22s22p63s23p64s23d4 (expected)
But this is not what happens!!
Chromium is actually:1s22s22p63s23p64s13d5
Why?This gives us two half filled
orbitals (the others are all still full)Half full is slightly lower in energy.The same principal applies to
copper.
Copper’s electron configuration
Copper has 29 electrons so we expect: 1s22s22p63s23p64s23d9
But the actual configuration is: 1s22s22p63s23p64s13d10
This change gives one more filled orbital and one that is half filled.
Remember these exceptions: d4, d9
Irregular configurations of Cr and Cu
Chromium steals a 4s electron to make its 3d sublevel HALF FULL
Copper steals a 4s electron to FILL its 3d sublevel
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
aufbau diagram  page 133
Electron Electron ConfigurationsConfigurations……
……are the way electrons are are the way electrons are arranged in various orbitals around arranged in various orbitals around the nuclei of atoms. the nuclei of atoms. Three rules Three rules tell us how:tell us how:
1)1) Aufbau principleAufbau principle  electrons enter  electrons enter the lowest energy first.the lowest energy first.
• This causes difficulties because of the This causes difficulties because of the overlap of orbitals of different overlap of orbitals of different energies – follow the diagram!energies – follow the diagram!
2)2) Pauli Exclusion PrinciplePauli Exclusion Principle  at most 2  at most 2 electrons per orbital  different electrons per orbital  different spinsspins
Pauli Exclusion Pauli Exclusion PrinciplePrinciple
No two electrons in an atom can have the same four quantum numbers.
Wolfgang Pauli
To show the different direction of spin, a pair in the same orbital is written as:
Quantum NumbersQuantum Numbers
Each electron in an atom has a unique set of 4 quantum numbers which describe it.
1) Principal quantum number2) Angular momentum quantum number3) Magnetic quantum number4) Spin quantum number
Electron ConfigurationsElectron Configurations)3)3Hund’s RuleHund’s Rule When electrons When electrons
occupy orbitals of equal occupy orbitals of equal energy, they don’t pair up until energy, they don’t pair up until
they have tothey have to..Let’s write the electron Let’s write the electron
configuration for Phosphorusconfiguration for Phosphorus We need to account for all 15 We need to account for all 15
electrons in phosphoruselectrons in phosphorus
The first two The first two electrons go into the electrons go into the
1s orbital1s orbital
Notice the opposite Notice the opposite direction of the spinsdirection of the spins
only 13 more to goonly 13 more to go......
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
The next electrons The next electrons go into the 2s go into the 2s
orbitalorbitalonly 11 moreonly 11 more......In
crea
sing
ene
rgy
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
• The next electrons go into the 2p orbital
• only 5 more...Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
• The next electrons go into the 3s orbital
• only 3 more...Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
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 (Hund’s)
• 3 unpaired electrons
• = 1s22s22p63s23p3
Orbitals fill in an orderOrbitals fill in an order Lowest energy to higher energyLowest energy to higher energy..Adding electrons can change the Adding electrons can change the
energy of the orbital. energy of the orbital. Full Full orbitalsorbitals are the absolute best are the absolute best
situationsituation..However,However, half filledhalf filled orbitals orbitals
have a lower energy, and are have a lower energy, and are next bestnext best
•Makes them more stableMakes them more stable..•Changes the filling orderChanges the filling order
Write the electron Write the electron configurations for these configurations for these
elementselements::Titanium  22 electronsTitanium  22 electrons
1s1s222s2s222p2p663s3s223p3p664s4s223d3d22
Vanadium  23 electronsVanadium  23 electrons1s1s222s2s222p2p663s3s223p3p664s4s223d3d33
Chromium  24 electronsChromium  24 electrons1s1s222s2s222p2p663s3s223p3p664s4s223d3d4 4 (expected)(expected)
But this is not what happensBut this is not what happens!!!!
Chromium is actuallyChromium is actually::1s1s222s2s222p2p663s3s223p3p664s4s113d3d55
WhyWhy??This gives us two This gives us two half filled half filled
orbitalsorbitals )the others are all still full))the others are all still full)Half full is slightly lower in Half full is slightly lower in
energyenergy..The same principal applies to The same principal applies to
coppercopper..
Copper’s electron Copper’s electron configurationconfiguration
Copper has 29 electrons so we Copper has 29 electrons so we expect: 1sexpect: 1s222s2s222p2p663s3s223p3p664s4s223d3d99
But the But the actual configurationactual configuration is is::1s1s222s2s222p2p663s3s223p3p664s4s113d3d1010
This change gives one more filled This change gives one more filled orbital and one that is half filledorbital and one that is half filled..
Remember these exceptions: Remember these exceptions: dd44, , dd99
Irregular configurations of Irregular configurations of Cr and CuCr and Cu
Chromium steals a 4s electron to make its 3d sublevel HALF FULL
Copper steals a 4s electron to FILL its 3d sublevel
7.12 Periodic 7.12 Periodic TrendsTrends
Ionization EnergyIonization Energy
An electron can be removed from an An electron can be removed from an atom if enough energy is absorbed atom if enough energy is absorbed (+)(+)
Ionization energyIonization energy – the energy – the energy required to remove one electron required to remove one electron from a gaseous neutral atomfrom a gaseous neutral atom
A (g) + energy A (g) + energy A A+ + (g) + e(g) + e
measurements of this are made on measurements of this are made on individual atoms in gas phase to individual atoms in gas phase to avoid interactions with nearby atoms avoid interactions with nearby atoms
Ionization EnergyIonization Energy
Ionization EnergyIonization Energy
if one electron is removed, the if one electron is removed, the positive charge binds the positive charge binds the electrons more tightly so 2electrons more tightly so 2ndnd ionization energy must be higherionization energy must be higher
the largest jump in energy is the largest jump in energy is when you remove a core electron when you remove a core electron instead of valenceinstead of valence
Ionization EnergyIonization Energy
Ionization EnergyIonization Energy
Across Period:Across Period: requires more requires more
energy to remove energy to remove an electron so an electron so increasesincreases
because because electrons added electrons added in the same in the same energy level do energy level do not shield not shield electrons from electrons from nuclear chargenuclear charge
Down Group:Down Group: requires less requires less
energy to energy to remove electron remove electron so decreasesso decreases
because the because the valence valence electrons are electrons are farther away farther away from protons from protons attracting themattracting them
Ionization EnergyIonization Energy
Ionization EnergyIonization Energy
Electron AffinityElectron Affinity
Electron AffinityElectron Affinity – the energy – the energy change when an electron is change when an electron is added to a gaseous neutral atomadded to a gaseous neutral atom exothermic ()exothermic ()
A + eA + e  A A + energy + energy
Electron AffinityElectron Affinity
Across Period:Across Period: releases more releases more
energy so number energy so number increases (gets increases (gets more negative)more negative)
because electrons because electrons added in the added in the same energy level same energy level do not shield do not shield electrons from electrons from nuclear chargenuclear charge
Down Group:Down Group: releases less releases less
energy so energy so number number decreases (gets decreases (gets less negative)less negative)
because the because the electrons being electrons being added are farther added are farther away from the away from the attracting attracting protonsprotons
Electron AffinityElectron Affinity
Atomic RadiiAtomic Radii
Defined by the edge Defined by the edge of its orbital but of its orbital but since the edges are since the edges are fuzzy, difficult to fuzzy, difficult to determinedetermine
Atomic RadiiAtomic Radii – half – half the distance between the distance between the nuclei of the nuclei of identical atoms that identical atoms that are bonded togetherare bonded together
Atomic RadiiAtomic Radii Across Period:Across Period:
atoms get smalleratoms get smaller because of the because of the
increased number increased number of protons of protons attracting the attracting the electronselectrons
the electrons added the electrons added in the same energy in the same energy level do not shield level do not shield electrons from electrons from nuclear chargenuclear charge
Down Group:Down Group: atoms get atoms get
largerlarger increasesincreases because the because the
energy levels energy levels being added to being added to the atomthe atom
Atomic/Ionic RadiiAtomic/Ionic Radii
Why is the periodic table shaped like it is and how are the elements arranged?
Elements are arranged according to atomic #
and e configuration.
Li: 3 e’s 1s2 2s1
Na: 11 e’s 1s2 2s2 2p6 3s1
K: 19 e’s 1s2 2s2 2p6 3s2 3p6 4s1
Paramagnetic or diamagnetic?
Valence orbitals: outer shell orbitals beyond the closest noblegas configuration
Valence electrons: “the ones that can react” (located in the valence orbitals).
Elements in a vertical row have the same number of valence electrons.
2A Be Mg Ca Sr Ba Ra
2s2
3s2
4s2
5s2
6s2
7s2
The other e’s are called core electrons and don’t react.
2A
2s22p5 F3s23p5 Cl4s24p5 Br5s25p5 I6s26p5 At
Atomic sizes:
Atomic size affects many properties, both physical and chemical
Li Be B C N O F
Na
Smaller
Smaller
WHY?
K
Ionization Energy:
The energy required to completely remove an e from an atom in its gaseous state.
Mg(g) Mg1+ + e 1st ionization energy
Mg1+(g) Mg2+ + e 2nd ionization energy
Question: Which of the above ionizations would have the highest ionization energy and why?
electron being lost: 1st 2nd 3rd 4th 5th 6th 7th
Increases
Increases
I.E. Overhead
Electron Affinites:
The energy change that occurs when an electron is added to a gaseous atom .
Cl(g) + e Cl(g) E = 349 kJ/mol
What does the negative value mean?
Electron affinity values
What is meant by metallic character?
Common Oxidation states: note the vertical similarities.
I2(s)Cl2(g)
Br2(l)
The Halogen Family:
Li KNa
Alkali Metal Family