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

http://college.hmco.com/chemistry/shared/media/zumdahl/visual/visual.html?name=ch12&vis=_v12l

Electromagnetic Electromagnetic SpectrumSpectrum

The Wave-like ElectronThe Wave-like 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 ss-1 -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, sec-1)

= 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 10-19 J

m10x400

)s/m10x00.3)(sJ10x62.6( E

9

834

E = 4.96 x 10-19 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 10-34-34 J*sJ*s

hE


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


hvE

vc c

v

hc

E

2mcE 2mc

hc

vm

h

shows that anything with both mass and velocity has a corresponding wavelength


In 1924, Louis de In 1924, Louis de Broglie Broglie

(French scientist)(French scientist) suggested that suggested that

matter has both matter has both particle-like and particle-like and wave-like wave-like 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 particle-likelarger objects are mostly particle-like smaller objects are mostly wave-likesmaller objects are mostly wave-like

…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 line-emission spectrum-line-emission 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 spectrum-continuous 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

H-H 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 Line-Emission H Line-Emission 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 state-ground state- lowest energy lowest energy

state of an atomstate of an atom excited state-excited 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 Line-Emission H Line-Emission 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


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


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..


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 n-1 has integer values from 0 to n-1 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


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

dumbbell-dumbbell-shapedshaped

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


d orbitals: 5: d orbitals: 5: 3d3dxzxz, , 3d3dyzyz, , 3d3dxyxy, , 3d3dx2-y2x2-y2, , 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


f orbitals: 7 typesf orbitals: 7 typesvarious shapesvarious shapesll value of 3 value of 3begin in n=4begin in n=4


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


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

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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...

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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

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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

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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


easi

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nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

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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

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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


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


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



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



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



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


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


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 noble-gas 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

Documents

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