ATOMIC ATOMIC STRUCTURESTRUCTURE

James Maxwell developed an James Maxwell developed an

elegant mathematical theory in elegant mathematical theory in

1864 to describe all forms of 1864 to describe all forms of

radiation in terms of oscillating or radiation in terms of oscillating or

wave-like electric and magnetic wave-like electric and magnetic

fields in space.fields in space.

Electromagnetic Electromagnetic RadiationRadiation

lightlight

microwavesmicrowaves

television and radio signalstelevision and radio signals

x-raysx-rays

Wavelength (λ)Wavelength (λ)

length length between between 2 successive 2 successive crestscrests

Frequency (Frequency ())

(nu), number of (nu), number of

cycles cycles per per

second second that pass that pass

a certain point in a certain point in

space (Hz-cycles space (Hz-cycles

per second)per second)

AmplitudeAmplitude

maximum maximum height height

of a wave as of a wave as

measured from measured from

the axis of the axis of

propagationpropagation

NodesNodes

points of points of zerozero amplitude amplitude

always occur at always occur at λ/2 for λ/2 for sinusoidalsinusoidalwaveswaves

VelocityVelocity

speed of wavespeed of wave

velocity = velocity = λ λ

C - the speed of lightC - the speed of light

2.99792458 [just call it 3] x 102.99792458 [just call it 3] x 1088 m/s m/s

ALL EM RADIATION TRAVELS AT ALL EM RADIATION TRAVELS AT

THIS SPEED! THIS SPEED!

I call it easy, you’ll call it a trick!I call it easy, you’ll call it a trick!

Notice that λ and Notice that λ and are are inversely inversely

proportional. proportional.

When one is large, the other is When one is large, the other is

small. small.

Exercise 1 Exercise 1 Frequency of Frequency of Electromagnetic RadiationElectromagnetic Radiation

The brilliant red colors seen in The brilliant red colors seen in

fireworks are due to the emission of fireworks are due to the emission of

light with wavelengths around 650 light with wavelengths around 650

nm when strontium salts such as nm when strontium salts such as

Sr(NOSr(NO33))22 and SrCO and SrCO33 are heated. are heated.

This can be easily demonstrated in This can be easily demonstrated in

the lab by dissolving one of these the lab by dissolving one of these

salts in methanol that contains a salts in methanol that contains a

little water and igniting the mixture little water and igniting the mixture

in an evaporating dish.in an evaporating dish.

Calculate the frequency of red Calculate the frequency of red light light

of wavelength 6.50 X 10of wavelength 6.50 X 1022 nm. nm.

SolutionSolution

v v = 4.61 X 10= 4.61 X 101414 Hz Hz

The Nature of MatterThe Nature of Matter

At the end of the 19th century, At the end of the 19th century,

physicists were feeling rather smug. physicists were feeling rather smug.

All of physics had been explained [or All of physics had been explained [or

so they thought]. Students were so they thought]. Students were

being discouraged from pursuing being discouraged from pursuing

physics as a career since all of the physics as a career since all of the major problems had been solved! major problems had been solved!

Matter and energy were distinct: Matter and energy were distinct:

Matter was a collection of Matter was a collection of particles. particles.

Energy was a collection of waves. Energy was a collection of waves.

Enter Max Planck stage left…..Enter Max Planck stage left…..

THE QUANTIZATION THE QUANTIZATION OF ENERGYOF ENERGY

"Ultraviolet Catastrophe""Ultraviolet Catastrophe"

the fact that a glowing hot the fact that a glowing hot object object

did not emit UV light as did not emit UV light as predictedpredicted

Max Planck solved the problem. Max Planck solved the problem.

He made an incredible He made an incredible assumption:assumption:

19001900

There is a minimum amount of There is a minimum amount of

energy that can be gained or energy that can be gained or lost lost

by an atom, and all energy by an atom, and all energy gained gained

or lost must be some integer or lost must be some integer

multiple, n, of that minimum.multiple, n, of that minimum.

Energy = n(hEnergy = n(h) )

where h is a proportionality where h is a proportionality

constant, Planck's constant, constant, Planck's constant,

h = 6.6260755 x 10h = 6.6260755 x 10-34-34 joule joule sec. sec.

Energy = n(hEnergy = n(h))

The The is the lowest frequency that is the lowest frequency that

can be absorbed or emitted by the can be absorbed or emitted by the

atom, and the minimum energy atom, and the minimum energy

change, hchange, h, is called a , is called a quantumquantum of of

energy. Think of it as a “packet” of energy. Think of it as a “packet” of

E equal to hE equal to h..

There is no such thing as a There is no such thing as a transfer transfer

of E in fractions of quanta, only of E in fractions of quanta, only in in

whole numbers of quanta.whole numbers of quanta.

Planck was able to calculate a Planck was able to calculate a

spectrum for a glowing body that spectrum for a glowing body that

reproduced the experimental reproduced the experimental

spectrum.spectrum.

His hypothesis applies to all His hypothesis applies to all

phenomena on the atomic and phenomena on the atomic and

molecular scale.molecular scale.

Exercise 2Exercise 2 The Energy of a PhotonThe Energy of a Photon

The blue color in fireworks is often The blue color in fireworks is often

achieved by heating copper(I) achieved by heating copper(I)

chloride (CuCl) to about 1200° C. chloride (CuCl) to about 1200° C.

The compound then emits blue The compound then emits blue light light

having a wavelength of 450 nm. having a wavelength of 450 nm.

What is the increment of What is the increment of energy energy

(the quantum) that is emitted (the quantum) that is emitted at at

4.50 X 104.50 X 1022 nm by CuCl? nm by CuCl?

SolutionSolution

= 4.41 X 10= 4.41 X 10-19-19 J J

The Photoelectric Effect The Photoelectric Effect and Albert Einsteinand Albert Einstein

In 1900 Albert Einstein was In 1900 Albert Einstein was working working

in the patent office in Bern, in the patent office in Bern,

Switzerland. This left him time Switzerland. This left him time to to

work on Physics.work on Physics.

He proposed that EM radiation itself He proposed that EM radiation itself

was quantized; he was a great fan was quantized; he was a great fan

of Planck’s work! of Planck’s work!

He proposed that EM could be He proposed that EM could be

viewed as a stream of “particles” viewed as a stream of “particles”

called called photonsphotons..

Photoelectric EffectPhotoelectric Effect

Light bombards the surface of a Light bombards the surface of a

metal and electrons are metal and electrons are ejected.ejected.

FrequencyFrequency

Minimum must be met, or alas, Minimum must be met, or alas, no no

action! action!

Once minimum is met, Once minimum is met, intensityintensity

increases rate of ejection.increases rate of ejection.

PhotonPhoton

massless particles of lightmassless particles of light

EEphotonphoton = = hh = = hchc

λλ

You know Einstein for the You know Einstein for the famous famous

E = mcE = mc22 from his second “work” from his second “work” as as

the special theory of relativity the special theory of relativity published in 1905. published in 1905.

Such blasphemy, energy has Such blasphemy, energy has mass?! mass?!

That would mean: m = That would mean: m = E E

cc22

Therefore, Therefore,

m = m = E E = = hc/λhc/λ = = h h

cc22 c c22 λc λc

Does a photon have Does a photon have mass?mass?

Yep! Yep!

In 1922 American physicist Arthur In 1922 American physicist Arthur Compton performed experiments Compton performed experiments involving collisions of X-rays and involving collisions of X-rays and electrons that showed photons do electrons that showed photons do exhibit the apparent mass exhibit the apparent mass calculated above.calculated above.

SummarySummary

Energy is quantized.Energy is quantized. It can occur only in discrete units It can occur only in discrete units

called quanta [hcalled quanta [h].]. EM radiation [light, etc.] exhibits EM radiation [light, etc.] exhibits

wave and particle properties.wave and particle properties. This phenomenon is known as the This phenomenon is known as the

dual nature of lightdual nature of light..

Since light which was thought to be Since light which was thought to be wavelike now has certain wavelike now has certain characteristics of particulate matter, characteristics of particulate matter, is the converse also true? is the converse also true?

Enter Louis de Broglie Enter Louis de Broglie

[French physicist, 1923] [French physicist, 1923]

stage right…stage right…

IF, IF,

m = m = h h

λcλc

substitute v [velocity] for c for any substitute v [velocity] for c for any

object NOT traveling at the speed of object NOT traveling at the speed of

light, then rearrange and solve for light, then rearrange and solve for

lambda.lambda.

This is called the de Broglie This is called the de Broglie equation:equation:

λ = λ = h h

mvmv

Exercise 3Exercise 3 Calculations of Calculations of WavelengthWavelengthCompare the wavelength for an Compare the wavelength for an

electron (mass = 9.11 X 10electron (mass = 9.11 X 10-31-31 kg) kg)

traveling at a speed of 1.0 X 10traveling at a speed of 1.0 X 1077 m/s m/s

with that for a ball (mass = 0.10 with that for a ball (mass = 0.10 kg) kg)

traveling at 35 m/s.traveling at 35 m/s.

λe λe = 7.27 X 10= 7.27 X 10-11-11 m m

λb λb = 1.9 X 10= 1.9 X 10-34-34 m m

SolutionSolution

The more massive the object, The more massive the object, the the

smaller its associated smaller its associated wavelength wavelength

and vice versa!and vice versa!

Davisson and Germer @ Bell labs Davisson and Germer @ Bell labs

found that a beam of electrons found that a beam of electrons was was

diffracted like light waves by the diffracted like light waves by the

atoms of a thin sheet of metal foil atoms of a thin sheet of metal foil

and that de Broglie's relation was and that de Broglie's relation was

followed quantitatively.followed quantitatively.

ANY moving ANY moving

particle has particle has

an an associated associated

wavelength.wavelength.

We now know that E is really a We now know that E is really a form form

of matter, and ALL matter shows of matter, and ALL matter shows

the same types of properties. the same types of properties.

That is, all matter exhibits both That is, all matter exhibits both

particulate and wave properties.particulate and wave properties.

Silly physicists!Silly physicists!

HYDROGEN’S ATOMIC HYDROGEN’S ATOMIC LINE SPECTRA LINE SPECTRA

and and

NIELS BOHRNIELS BOHR

Emission SpectrumEmission Spectrum

the collection of frequencies of the collection of frequencies of light light

given off by an "excited" given off by an "excited" electronelectron

Line SpectrumLine Spectrum

Isolate a thin beam by passing Isolate a thin beam by passing

through a slit then a prism or a through a slit then a prism or a

diffraction grating which sorts diffraction grating which sorts into into

discrete frequencies or lines.discrete frequencies or lines.

Johann BalmerJohann Balmer

worked out a worked out a mathematical mathematical relationship that relationship that accounted for accounted for the 3 lines of the 3 lines of longest wavelength in the longest wavelength in the

visible visible emission spectrum of H. (red, emission spectrum of H. (red, green and blue lines)green and blue lines)

Niels Bohr connected spectra, and Niels Bohr connected spectra, and

the quantum ideas of Einstein and the quantum ideas of Einstein and

Planck: Planck:

The single electron of the The single electron of the hydrogen hydrogen

atom could occupy only certain atom could occupy only certain

energy statesenergy states, , stationary statesstationary states..

"Big Mamma "Big Mamma Assumption"Assumption"

An electron in an atom would An electron in an atom would

remain in its lowest E state remain in its lowest E state unlessunless

otherwise disturbed.otherwise disturbed.

Energy is Energy is

absorbed or absorbed or

emitted by a emitted by a

change from change from

this state.this state.

An electron with n = 1 has the An electron with n = 1 has the most most

negative energy and is thus the negative energy and is thus the most strongly attracted to the most strongly attracted to the nucleus. nucleus.

[Higher states have less negative [Higher states have less negative values and are not as strongly values and are not as strongly attracted.]attracted.]

Ground StateGround State

n = 1, for hydrogenn = 1, for hydrogen

To move from ground to n = 2, the To move from ground to n = 2, the

electron/atom must absorb electron/atom must absorb no more no more

or no less thanor no less than 0.75 Rhc. [that’s a 0.75 Rhc. [that’s a

collection of constants]collection of constants]

So, a move of n = 2 to n = 1 So, a move of n = 2 to n = 1 emitsemits 985 kJ of energy.985 kJ of energy.

What goes up must come down. What goes up must come down.

Energy absorbed must eventually Energy absorbed must eventually be be

emitted.emitted.

hc

= h = Ephoton

The origin or atomic line spectra is The origin or atomic line spectra is

the movement of electrons between the movement of electrons between

quantized energy states.quantized energy states.

IF an electron moves from higher to IF an electron moves from higher to

lower E states, a photon is lower E states, a photon is

emittedemitted and an emission line is and an emission line is

observed.observed.

Bohr’s equation for calculating Bohr’s equation for calculating

the energy of the E levels the energy of the E levels available available

to the electron in the hydrogen to the electron in the hydrogen

atom:atom:

2

21810178.2

n

ZJxE

where n is an integer [larger n where n is an integer [larger n

means larger orbit radius, farther means larger orbit radius, farther

from nucleus], and Z is the nuclear from nucleus], and Z is the nuclear

charge.charge.

2

21810178.2

n

ZJxE

The NEGATIVE sign simply means The NEGATIVE sign simply means

that the E of the electron bound to that the E of the electron bound to

the nucleus is lower that it world the nucleus is lower that it world be be

if the electron were at an infinite if the electron were at an infinite

distance [n = ∞] from the nucleus distance [n = ∞] from the nucleus

where there is NO interaction and where there is NO interaction and

the energy is zero.the energy is zero.

E is simply the subtraction of E is simply the subtraction of

calculating the energy of two calculating the energy of two

different levels, say n=6 and n=1. different levels, say n=6 and n=1.

If the difference is negative, E was If the difference is negative, E was

lost. If the difference is positive, E lost. If the difference is positive, E

was gained. was gained.

Only works for elements with Only works for elements with ONE ONE

electron. electron.

Secondly, the electron Secondly, the electron DOES DOES NOTNOT

orbit the nucleus in a fixed orbit the nucleus in a fixed path!!path!!

Major defect in Bohr's Major defect in Bohr's theory:theory:

Exercise 4Exercise 4Energy Quantization in Energy Quantization in HydrogenHydrogenCalculate the energy required to Calculate the energy required to excite the hydrogen electron from excite the hydrogen electron from level n = 1 to level n = 2.level n = 1 to level n = 2.

Also calculate the wavelength of Also calculate the wavelength of light light

that must be absorbed by a that must be absorbed by a hydrogen hydrogen

atom in its ground state to reach atom in its ground state to reach this this

excited state.excited state.

SolutionSolution

∆∆E = 1.633 X 10E = 1.633 X 10-18-18 J J

λλ = 1.216 X 10 = 1.216 X 10-7-7 m m

Exercise 5Exercise 5 Electron Energies Electron Energies

Calculate the energy required Calculate the energy required to to

remove the electron from a remove the electron from a

hydrogen atom in its ground hydrogen atom in its ground state.state.

SolutionSolution

∆∆E = 2.178 X 10E = 2.178 X 10-18-18 J J

THE WAVE THE WAVE PROPERTIES OF THE PROPERTIES OF THE

ELECTRONELECTRON

Schrodinger, Heisenberg, Schrodinger, Heisenberg,

and and

Quantum NumbersQuantum Numbers

After World War IAfter World War I

Niels Bohr assembled a group of Niels Bohr assembled a group of

physicists in Copenhagen hoping physicists in Copenhagen hoping to to

derive a comprehensive theory for derive a comprehensive theory for

the behavior of electrons in atoms the behavior of electrons in atoms

from the viewpoint of the electron from the viewpoint of the electron

as a particle.as a particle.

Erwin Schrodinger independently Erwin Schrodinger independently

tried to accomplish the same tried to accomplish the same thing thing

but focused on de Broglie's but focused on de Broglie's

equation and the electron as a equation and the electron as a

wave. wave.

Schrodinger's approach was Schrodinger's approach was better, better,

explained more than Bohr's, and explained more than Bohr's, and

met with more success. met with more success.

Quantum mechanics was born!Quantum mechanics was born!

de Broglie opened a can of worms de Broglie opened a can of worms

among physicists by suggesting among physicists by suggesting the the

electron had wave properties.electron had wave properties.

The electron has dual properties.The electron has dual properties.

Werner Heisenberg and Max Born Werner Heisenberg and Max Born provided the provided the uncertainty principle.uncertainty principle.

……if you want to define the if you want to define the momentum then you have to forego momentum then you have to forego knowledge of its exact position at the knowledge of its exact position at the time of the measurement.time of the measurement.

if we choose to know the energy if we choose to know the energy of an of an

electron in an atom with only a electron in an atom with only a small small

uncertainty, then we must accept uncertainty, then we must accept a a

correspondingly large uncertainty correspondingly large uncertainty

about its position in the space about its position in the space about about

the atom's nucleus. the atom's nucleus.

Max Born, on the basis of Max Born, on the basis of Heisenberg's work Heisenberg's work suggested:suggested:

So What?So What?

We can only calculate the We can only calculate the

probabilityprobability of finding an of finding an electron electron

within a given space.within a given space.

THE WAVE THE WAVE MECHANICAL VIEW OF MECHANICAL VIEW OF

THE ATOMTHE ATOM

Schrodinger EquationSchrodinger Equation

Solutions are Solutions are called called

wave functions—wave functions—

chemically chemically important. important.

The electron is characterized as The electron is characterized as a a

matter-wave.matter-wave.

Sort of standing waves --Sort of standing waves --

only certain allowed wave only certain allowed wave functions.functions.

Each ψ for the electron Each ψ for the electron

in the H atom in the H atom corresponds corresponds

to an allowed energy to an allowed energy

(-Rhc/n(-Rhc/n22). ).

For each integer n, there For each integer n, there

is an atomic state is an atomic state

characterized by its own characterized by its own

ψ and energy Eψ and energy Enn..

Points 1 & 2 above say Points 1 & 2 above say

the energy of electrons the energy of electrons

is quantized. is quantized.

Notice in the figure to Notice in the figure to

the right, that only the right, that only whole whole

numbers of standing numbers of standing

waves can “fit” in the waves can “fit” in the

proposed orbits.proposed orbits.

The hydrogen electron isThe hydrogen electron isvisualized as a standing visualized as a standing wave around the nucleus wave around the nucleus [left]. The circumference of [left]. The circumference of a particular circular orbit a particular circular orbit would have to correspond to would have to correspond to a whole number of a whole number of wavelengths, as shown in wavelengths, as shown in

(a) (a) and (b), OR else destructive and (b), OR else destructive interference occurs, as interference occurs, as shown in (c). shown in (c).

This is consistent with the fact that This is consistent with the fact that only certain electron energies are only certain electron energies are allowed; the atom is quantized. allowed; the atom is quantized. (Although this idea encouraged (Although this idea encouraged scientists to use a wave theory, it scientists to use a wave theory, it does not mean that the electron does not mean that the electron really travels in circular orbits.)really travels in circular orbits.)

The square of ψ gives The square of ψ gives

the intensity of the the intensity of the

electron wave or the electron wave or the

probabilityprobability of finding of finding

the electron at the the electron at the

point P in space about point P in space about

the nucleus—the the nucleus—the

intensity of color in intensity of color in

(a) above represents the probability (a) above represents the probability

of finding the electron in that space.of finding the electron in that space.

Electron density map, electron Electron density map, electron

density, and electron probability density, and electron probability ALL ALL

mean the same thing! mean the same thing!

Matter-waves for allowed energy Matter-waves for allowed energy

states are also called (drum roll states are also called (drum roll

please…) orbitals.please…) orbitals.

To solve Schrodinger's equation in a To solve Schrodinger's equation in a

3-dimensional world we need the 3-dimensional world we need the

quantum numbers n, l, and mquantum numbers n, l, and mℓℓ..

The amplitude of the electron wave at The amplitude of the electron wave at

a point depends on the distance of the a point depends on the distance of the

point from the nucleus.point from the nucleus.

Imagine that the space around an Imagine that the space around an

H nucleus is made up of a series H nucleus is made up of a series

of thin “shells” like the layers of of thin “shells” like the layers of

an onion.an onion.

Plot the total probability of finding Plot the total probability of finding

the electron in each shell versus the electron in each shell versus the the

distance from the nucleus. distance from the nucleus.

The maximum in the curve occurs The maximum in the curve occurs

because of two opposing effects. because of two opposing effects.

1) The probability of finding an 1) The probability of finding an

electron is greatest near the electron is greatest near the nucleus nucleus

[just can’t resist the attraction of a [just can’t resist the attraction of a

proton!], proton!],

BUT… BUT…

2) the volume of the spherical 2) the volume of the spherical shell shell

increases with distance from the increases with distance from the

nucleus.nucleus.

SO…SO…

We are summing more positions We are summing more positions of of

possibility, so the TOTAL possibility, so the TOTAL probability probability

increases to a certain radius and increases to a certain radius and then then

decreases as the electron decreases as the electron probability probability

at EACH position becomes very at EACH position becomes very small.small.

Try not to stress over this! It’s my Try not to stress over this! It’s my

moral obligation to TRY to explain it moral obligation to TRY to explain it

to you. Stress over quantum to you. Stress over quantum

numbers and electron numbers and electron

configurations and periodicity if you configurations and periodicity if you

must—that’s the important stuff in must—that’s the important stuff in

this chapter!this chapter!

Quantum Numbers & Quantum Numbers & Atomic Atomic Orbitals OrbitalsThe value of n limits the The value of n limits the

possible possible

values of values of ℓℓ, which in turn limit , which in turn limit the the

values of mvalues of mℓℓ..

n--principal: n--principal: 1 to infinity 1 to infinity

Determines the total energy of Determines the total energy of the the

electron. electron.

Most probable [within 90%] Most probable [within 90%] distance distance

of the electron from the nucleus. of the electron from the nucleus.

A measure of the orbital size or A measure of the orbital size or

diameter. diameter.

2n2n22 electrons may be assigned electrons may be assigned to a to a

shell.shell.

It’s simply the Energy level that It’s simply the Energy level that

the electron is in. the electron is in.

If it’s a 3s electron, n = 3, If it’s a 3s electron, n = 3,

if it’s a 4d electron, n = 4, etc.if it’s a 4d electron, n = 4, etc.

ℓℓ--angular momentum:--angular momentum: 0,1,2,....(n-1) 0,1,2,....(n-1)

Electrons within a shell may be Electrons within a shell may be

grouped into subshells [or sublevels, grouped into subshells [or sublevels,

same thing!], each characterized by same thing!], each characterized by

its certain wave shape -- n its certain wave shape -- n possibilities. possibilities.

Each Each ℓℓ is a different orbital shape or is a different orbital shape or

orbital type. orbital type.

n limits n limits ℓℓ to no larger than n-1. to no larger than n-1.

Thus, the number of possibilities for Thus, the number of possibilities for

ℓℓ is equal to n. is equal to n.

(English translation: 3 sublevels for (English translation: 3 sublevels for

3rd E level, 4 for 4th E level, etc.) 3rd E level, 4 for 4th E level, etc.)

spdf spdf 0123 0123

sharp, principle,sharp, principle,diffuse, fundamentaldiffuse, fundamental- early days of atomic - early days of atomic spectroscopyspectroscopy

You can keepgoing from

g …

mmℓℓ--magnetic--magnetic

Assign the “blanks” in orbital notation Assign the “blanks” in orbital notation

with zero on the middle blank and with zero on the middle blank and

then –then –ℓ ℓ through zero tothrough zero to +ℓ. +ℓ. I’ll bet this I’ll bet this

looks familiar for Sulfur from Chem. I!looks familiar for Sulfur from Chem. I!

That means that the range is That means that the range is from from

+ to - + to - ℓℓ..

It describes the orientation of an It describes the orientation of an

orbital in a given subshell.orbital in a given subshell.

The down arrow in the 3p, -1 slot is The down arrow in the 3p, -1 slot is

the last electron placed [valence the last electron placed [valence

electron]. So far, it’s set of quantum electron]. So far, it’s set of quantum

numbers is 3, 1, -1.numbers is 3, 1, -1.

Exercise 6Exercise 6 Electron Subshells Electron SubshellsFor principal quantum level n = For principal quantum level n =

5, 5,

determine the number of determine the number of allowed allowed

subshells (different values of subshells (different values of ℓ), ℓ), and and

give the designation of each.give the designation of each.

SolutionSolution

ℓ ℓ = 0; 5s= 0; 5s

ℓ ℓ = 1; 5p= 1; 5p

ℓ ℓ = 2; 5d= 2; 5d

ℓ ℓ = 3; 5f= 3; 5f

ℓ ℓ = 4; 5g= 4; 5g

The Shapes of Atomic The Shapes of Atomic Orbitals Orbitals

There is no sharp boundary There is no sharp boundary beyond beyond

which the electrons are never which the electrons are never

found!!found!!

s--sphericals--spherical

The size increases The size increases

with n. The nodes with n. The nodes

you see represent you see represent

ZERO probability of ZERO probability of

finding the electron in that finding the electron in that region region

of space. The number of nodes of space. The number of nodes

equals n-1 for s orbitals.equals n-1 for s orbitals.

pp

Have one plane that slices through Have one plane that slices through

the nucleus and divides the region the nucleus and divides the region

of electron density into 2 halves. of electron density into 2 halves.

3 orientations: px, py, and pz.3 orientations: px, py, and pz.

Nodal planeNodal plane

The electron can never be The electron can never be found found

there!!there!!

d--2 nodal planes slicing through d--2 nodal planes slicing through

the nucleus to create four the nucleus to create four sections; sections;

5 orbitals. 5 orbitals.

The dzThe dz22 orbital is really strange! orbital is really strange!

f--3 nodal planes slicing through f--3 nodal planes slicing through the the

nucleus; eight sections; 7 nucleus; eight sections; 7 orbitalsorbitals

Electron ConfigurationsElectron Configurations

Chemical properties depend on Chemical properties depend on the the

number and arrangement of number and arrangement of

electrons in an atom. Usually electrons in an atom. Usually only only

the valence electrons play the the valence electrons play the

reaction game.reaction game.

Electron SpinElectron Spin

1920--chemists 1920--chemists

realized that since realized that since

electrons interact electrons interact

with a magnetic with a magnetic

field, there must be field, there must be

one more concept to explain one more concept to explain the the

behavior of electrons in atoms.behavior of electrons in atoms.

accounts for the reaction of accounts for the reaction of

electrons in a magnetic field.electrons in a magnetic field.

mmss--the 4th Quantum --the 4th Quantum NumberNumber

MagnetismMagnetism

magnetitemagnetite--Fe--Fe33OO44, natural , natural

magnetic oxide of ironmagnetic oxide of iron

NEVER FORGET: NEVER FORGET:

opposites attract & likes repelopposites attract & likes repel

1600--William 1600--William

Gilbert concluded Gilbert concluded

the earth is also a the earth is also a

large spherical large spherical

magnet with magnet with

magnetic southmagnetic south at at

the north pole the north pole

(Santa's habitat).(Santa's habitat).

PARAMAGNETISMPARAMAGNETISM

AND UNPAIRED ELECTRONSAND UNPAIRED ELECTRONS

DiamagneticDiamagnetic

not magnetic [magnetism not magnetic [magnetism didies] es]

In fact, they are In fact, they are slightlyslightly repelled. repelled.

All electrons are PAIRED.All electrons are PAIRED.

ParamagneticParamagnetic

attracted to a magnetic field attracted to a magnetic field

lose their magnetism when lose their magnetism when removed removed

from the magnetic fieldfrom the magnetic field

HAS ONE OR MORE UNPAIRED HAS ONE OR MORE UNPAIRED ELECTRONSELECTRONS

FerromagneticFerromagnetic

retain magnetism upon retain magnetism upon introduction introduction

to, then removal from a to, then removal from a magnetic magnetic

fieldfield

All of these are explained All of these are explained by electron spins…by electron spins…

1) Each electron has a magnetic 1) Each electron has a magnetic field with N & S poles.field with N & S poles.

2) Electron spin is quantized such 2) Electron spin is quantized such that, in an external magnetic that, in an external magnetic field, only two orientations of field, only two orientations of the electron magnet and its the electron magnet and its spin are possible.spin are possible.

3) +/- 1/23) +/- 1/2

H is paramagnetic. H is paramagnetic.

He is diamagnetic. He is diamagnetic.

WHY?WHY?

H has one H has one unpairedunpaired electron. electron.

He has He has NONO unpaired unpaired electrons; electrons; all all

spins offset and cancel each spins offset and cancel each other other

out.out.

What about What about ferromagnetic?ferromagnetic?

Clusters of atoms have their Clusters of atoms have their

unpaired electrons aligned within unpaired electrons aligned within a a

cluster. Clusters are more or less cluster. Clusters are more or less

aligned and substance acts as a aligned and substance acts as a

magnet. magnet.

Don't drop it!!Don't drop it!!

When all of When all of the the

domains, domains,

represented represented by by

these arrows these arrows

are aligned, it are aligned, it

behaves as a behaves as a

magnet. magnet.

This is what This is what

happens if you happens if you

drop it! drop it!

The domains go The domains go

in different in different

directions and it directions and it

no longer no longer

operates as a operates as a

magnet.magnet.

The Pauli Exclusion The Pauli Exclusion PrinciplePrinciple

In 1925 Wolfgang Pauli stated: In 1925 Wolfgang Pauli stated:

No two electrons in an atom can No two electrons in an atom can

have the same set of four quantum have the same set of four quantum

numbersnumbers. This means no atomic . This means no atomic

orbital can contain more than 2 orbital can contain more than 2

electrons & they must be of electrons & they must be of opposite opposite

spin!!spin!!

ATOM ORBITAL ATOM ORBITAL ENERGIESENERGIES

AND ELECTRON AND ELECTRON ASSIGNMENTSASSIGNMENTS

The value of n (E = -Rhc/nThe value of n (E = -Rhc/n22) )

determines the energy of an determines the energy of an electron.electron.

Many-electron atoms depend on Many-electron atoms depend on both both

n & n & ℓℓ..

Order of Orbital EnergiesOrder of Orbital Energies

Use the diagonal rule or Aufbau Use the diagonal rule or Aufbau series.series.

Orbital radius changes slightly with Orbital radius changes slightly with ℓℓ as well as with n.as well as with n.

Subshell orbitals contract toward the Subshell orbitals contract toward the nucleus as the value of nucleus as the value of ℓℓ increases. increases.

Contraction is partially into the volume Contraction is partially into the volume of space occupied by the of space occupied by the corecore electrons.electrons.

The energy of these subshells’ The energy of these subshells’

electrons is raised by the repulsion electrons is raised by the repulsion

between the subshell electrons and between the subshell electrons and

the core electrons.the core electrons.

A subshell's energy rises as its A subshell's energy rises as its ℓℓ

quantum number increases when quantum number increases when

inner electrons are present.inner electrons are present.

Order of Orbital Order of Orbital AssignmentsAssignments

Each electron is lazy and occupies Each electron is lazy and occupies the lowest energy space available.the lowest energy space available.

Based on the assumption that Based on the assumption that inner inner

electrons have no effect on which electrons have no effect on which orbitals are assigned to outer or orbitals are assigned to outer or valence electrons.valence electrons.

Not exactly true …Not exactly true … (use diagonal rule) (use diagonal rule)

electron configurations electron configurations

(spectroscopic notation)(spectroscopic notation)

clump the 1's, 2's, etc. clump the 1's, 2's, etc. TOGETHERTOGETHER

Hunds RuleHunds Rule

The The most stablemost stable arrangement of arrangement of

electrons is that with the maximum electrons is that with the maximum

number of unpaired electrons. number of unpaired electrons.

Minimizes electron-electron Minimizes electron-electron

repulsionsrepulsions ( (everyone gets their own everyone gets their own

room)room)

All single electrons also have All single electrons also have

parallel spins to reduce eparallel spins to reduce e--/e/e--

repulsions (aligns repulsions (aligns micromagnets).micromagnets).

When 2 electrons occupy the When 2 electrons occupy the same same

orbital they must have opposite orbital they must have opposite

spins (Pauli exclusion principle). spins (Pauli exclusion principle).

This helps to minimize eThis helps to minimize e--/e/e--

repulsions.repulsions.

Personally, I think this whole Personally, I think this whole

quantum number thing is quantum number thing is easiest easiest

when we start with the electron when we start with the electron

configurations, THEN write the configurations, THEN write the

quantum numbers. quantum numbers.

Allow me to recap: Allow me to recap: Don’t try to make this hard! Don’t try to make this hard!

It just isn’t.It just isn’t.

The first electron placed in an The first electron placed in an orbital gets the +1/2 and the orbital gets the +1/2 and the second one gets the -1/2.second one gets the -1/2.

Let’s practice:Let’s practice:

Give the electron configurations for Give the electron configurations for

the elements within this figure. the elements within this figure.

I’ll get you started!I’ll get you started!

S: 1sS: 1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p44

Cd:Cd:

La:La:

Hf:Hf:

Ra:Ra:

Ac:Ac:

And their Orbital And their Orbital Notation:Notation:

Sulfur:Sulfur:

Cd:Cd:

La:La:

Hf:Hf:

Ra:Ra:

Ac:Ac:

As electrons As electrons enter these enter these sublevels, their sublevels, their wave functions wave functions interfere with interfere with each other each other causing the energy of these to causing the energy of these to change and separate. change and separate.

Do not be misled by this diagram, Do not be misled by this diagram, there ARE INDEED energy there ARE INDEED energy differences between all of these differences between all of these sublevels.sublevels.

There is a super cool animation There is a super cool animation that that

illustrates this concept. The illustrates this concept. The website website

is from the Chief Reader of the is from the Chief Reader of the AP AP

Exam. This site is:Exam. This site is:

http://intro.chem.okstate.edu/http://intro.chem.okstate.edu/APnew/Default.html APnew/Default.html

Click on Electron Configuration Click on Electron Configuration

Animation. You’ll need the Animation. You’ll need the

shockwave plug-in. Once the shockwave plug-in. Once the

animation comes up, click on the animation comes up, click on the

screen to advance from screen to advance from Hydrogen Hydrogen

on up by atomic number. on up by atomic number.

What are the quantum numbers What are the quantum numbers for for

the outermost [valence] electron?the outermost [valence] electron?

S ?S ?Cd ?Cd ?La ?La ?Hf ?Hf ?Ra ?Ra ?Ac ?Ac ?

SulfurSulfur

Since the last electron put in is Since the last electron put in is #16 #16

and it is in the 3p sublevel, n = and it is in the 3p sublevel, n = 3 3

and and ℓ = 2. ℓ = 2.

It’s in the -1 slot, the mIt’s in the -1 slot, the mℓℓ = -1. = -1.

And, since it’s the second arrow And, since it’s the second arrow

placed [down arrow] its mplaced [down arrow] its mss = -1/2. = -1/2.

So the set of quantum numbers for So the set of quantum numbers for

the 16th electron in sulfur is: 3,2,-the 16th electron in sulfur is: 3,2,-1, 1,

-1/2.-1/2.

You accepted that the sublevels had You accepted that the sublevels had

differences in energies long ago. differences in energies long ago.

You even know the increasing order You even know the increasing order

of energies:of energies:

s < p < d < f < g…s < p < d < f < g…

Now you have to be able to Now you have to be able to

EXPLAIEXPLAIN IT

on the AP test. on the AP test.

Throughout this discussion, keep Throughout this discussion, keep

some fundamental scientific some fundamental scientific

principles close at hand:principles close at hand:

– electrons repel each otherelectrons repel each other– electrons are attracted by the electrons are attracted by the

positive nucleuspositive nucleus– forces dissipate with forces dissipate with

increasing distance.increasing distance.

We need to We need to

examine the examine the

graph at the graph at the

right, radial right, radial

probabilities, probabilities,

again. again. mighty close to

the nucleus.“ZAPPED”

“penetrates”closest tothe nucleus

See the small hump near the See the small hump near the origin? origin?

That’s the That’s the

distance fromdistance from

the nucleus thatthe nucleus that

a 2s electron a 2s electron

occupies a occupies a

small but small but

significant significant

amount of the time.amount of the time.

mighty close to the nucleus.“ZAPPED”

“penetrates”closest tothe nucleus

We say the electron “penetrates We say the electron “penetrates to to

the nucleus” more than for the the nucleus” more than for the 2p 2p

orbital.orbital.

This causes a 2s electron to be This causes a 2s electron to be

ATTRACTED to the nucleus more ATTRACTED to the nucleus more

than a 2p electron making the than a 2p electron making the 2s 2s

orbital LOWER in E than the 2p orbital LOWER in E than the 2p

orbital.orbital.

Think of the nucleus as Think of the nucleus as “zapping” “zapping”

the energy of the electrons that the energy of the electrons that

penetrate closer to it. penetrate closer to it.

[Just don’t write that!][Just don’t write that!]

Imagine a hyper child—it’s on its Imagine a hyper child—it’s on its best behavior, sitting still, being best behavior, sitting still, being quiet, etc. when it’s close to Mom. quiet, etc. when it’s close to Mom.

The closer to the Mother Nucleus the The closer to the Mother Nucleus the hyper electron is, the less hyper or hyper electron is, the less hyper or energetic it is. energetic it is.

Don’t EVER write this as an Don’t EVER write this as an answer answer

to an essay question! It’s just a to an essay question! It’s just a

model to help you get your model to help you get your teeth in teeth in

to this concept!to this concept!

Same song second Same song second verse…verse…

The last hump represents the The last hump represents the greatest greatest

probability for predicting the probability for predicting the

distance of an electron from the distance of an electron from the

nucleus, BUT the first humps nucleus, BUT the first humps

determine the order of the determine the order of the energy. energy.

The top graph is The top graph is

for 3s—note it for 3s—note it

has 2 humps has 2 humps close close

to the nucleusto the nucleus

The bottom graph The bottom graph

is for 3s, 3p and is for 3s, 3p and

note that 3d only note that 3d only

has one hump.has one hump.

3s penetrates most [has least energy], 3s penetrates most [has least energy],

then 3p [higher than 3s, lower than then 3p [higher than 3s, lower than 3d] 3d]

then 3d penetrates least [so it has the then 3d penetrates least [so it has the highest energy].highest energy].

Moral:Moral:

The greater the penetration, the The greater the penetration, the

less energy that orbital has. less energy that orbital has.

Since you already knew the order Since you already knew the order

with respect to energy, with respect to energy,

s < p < d < f s < p < d < f

the degree of penetration is: the degree of penetration is:

s’s penetrate s’s penetrate mostmost and f’s and f’s penetrate penetrate

leastleast..

Ion Orbital Energies and Ion Orbital Energies and Electron ConfigurationsElectron Configurations

The dfs overlay [that thing that The dfs overlay [that thing that happens when the configurations don’t happens when the configurations don’t fit the pattern in transition metals and fit the pattern in transition metals and rare earth metals] does not occur in rare earth metals] does not occur in ion configurations since the valence ion configurations since the valence ((outermost n)outermost n) electrons are the first to electrons are the first to go! go!

The shell energy ranges The shell energy ranges separate separate

more widely as electrons are more widely as electrons are

removed.removed.

Atoms and ions with unpaired Atoms and ions with unpaired

electrons are paramagnetic electrons are paramagnetic (attracted (attracted

to a magnetic field).to a magnetic field).

Transition metals with +2 or higher Transition metals with +2 or higher

have no ns electrons.have no ns electrons.

FeFe+2+2 is paramagnetic to the extent of is paramagnetic to the extent of

4 unpaired electrons and Fe4 unpaired electrons and Fe+3+3 is is

paramagnetic to the extent of 5 paramagnetic to the extent of 5

unpaired electrons.unpaired electrons.

THE HISTORY OF THE THE HISTORY OF THE PERIODIC TABLEPERIODIC TABLE

1800ish--Johann Dobereiner -- triads 1800ish--Johann Dobereiner -- triads 1864 -- John Newlands -- octaves 1864 -- John Newlands -- octaves 1870--Dmitrii Mendeleev & Julius 1870--Dmitrii Mendeleev & Julius Lothar Meyer--by mass Lothar Meyer--by mass 1913 -- Mosley--by number of protons1913 -- Mosley--by number of protons

Group IAGroup IA

(1A or 1)(1A or 1)

--alkali metals--alkali metals

Group IIAGroup IIA

(2A or 2)(2A or 2)

--alkaline earth --alkaline earth

metalsmetals

Group VIAGroup VIA

(6A or 16)(6A or 16)

-- Chalcogens-- Chalcogens

Group VIIAGroup VIIA

(7A or 17)(7A or 17)

-- Halogens-- Halogens

Group VIIIA Group VIIIA

(8A or 18)(8A or 18)

-- Noble gas-- Noble gas

Some Properties of Some Properties of Common Groups: Common Groups:

the most reactive metal familythe most reactive metal family

must be stored under oilmust be stored under oil

react with water violently!react with water violently!

Alkali MetalsAlkali Metals

Alkaline-earth MetalsAlkaline-earth Metals

Except for Be(OH)Except for Be(OH)22, the metal , the metal

hydroxides formed by this group hydroxides formed by this group

provide basic solutions in water. provide basic solutions in water.

Pastes of these used in batteries.Pastes of these used in batteries.

many found combined with many found combined with metal metal

oresores

Chalcogen FamilyChalcogen Family

Halogen FamilyHalogen Family

known as the “salt-formers”known as the “salt-formers”

used in modern lightingused in modern lighting

Noble Gas FamilyNoble Gas Family

known for their disinterest in known for their disinterest in other other

elements elements

once thought to never reactonce thought to never react

neon used to make bright signsneon used to make bright signs

Transition metalsTransition metals

——fill the d orbitals. fill the d orbitals.

Anomalies occur at Chromium Anomalies occur at Chromium and and

Copper to Copper to minimize minimize electron/electron electron/electron

repulsionsrepulsions. .

If you learned that there is If you learned that there is special special

stability associated with a half-stability associated with a half-filled filled

sub-level, IT’S A LIE!!sub-level, IT’S A LIE!!

No such stability exists! No such stability exists!

It’s all about lowering energy It’s all about lowering energy by by

minimizing electron/electron minimizing electron/electron

repulsions.repulsions.

Rare Earth Metals Rare Earth Metals --fill the d sublevels--fill the d sublevels

Lanthanides and Lanthanides and ActinidesActinides

These sometimes put an electron in These sometimes put an electron in d d

[just one or two electrons] before [just one or two electrons] before filling f. filling f.

This is that dsf overlay referred to This is that dsf overlay referred to earlier—the energies of the sublevels earlier—the energies of the sublevels are very similar.are very similar.

Periodic TrendsPeriodic Trends

A trend is A trend is NOTNOT an EXPLANATION! an EXPLANATION!

This an important section—there is This an important section—there is

almost always an essay involving almost always an essay involving

this topic on the AP exam.this topic on the AP exam.

There are several arguments you will There are several arguments you will

evoke to EXPLAIN a periodic trend. evoke to EXPLAIN a periodic trend.

Remember opposites attract and likes Remember opposites attract and likes

repel. The trick is learning which repel. The trick is learning which

argument to use when explaining a argument to use when explaining a

certain trend!certain trend!

Effective Nuclear Charge, Effective Nuclear Charge, Z Zeffeff

Essentially equal to the group Essentially equal to the group

number. number.

Think of the IA’s having a ZThink of the IA’s having a Zeffeff of of one one

while the VII A’s have a Zwhile the VII A’s have a Zeffeff of 7! of 7!

The idea is that the higher the ZThe idea is that the higher the Zeffeff,,the more attractive force there is the more attractive force there is emanating from the nucleus, drawing emanating from the nucleus, drawing electrons in or holding them in place. electrons in or holding them in place.

Relate this to ENERGY whenever Relate this to ENERGY whenever possible. possible.

DistanceDistance

Attractive forces dissipate with Attractive forces dissipate with

increased distance. increased distance.

Relate this to ENERGY Relate this to ENERGY whenever whenever

possible.possible.

ShieldingShielding

Electrons in the “core” effectively Electrons in the “core” effectively

shield the nucleus’ attractive shield the nucleus’ attractive force force

for the valence electrons. for the valence electrons.

Use this ONLY when going up and Use this ONLY when going up and

down the tabledown the table, NOT across. , NOT across.

There is ineffective shielding There is ineffective shielding within within

a sublevel or energy level. a sublevel or energy level.

Relate this to ENERGY whenever Relate this to ENERGY whenever

possible. possible.

Dodge Ball – Dodge Ball – Such a Barbaric Such a Barbaric RitualRitualSince you’re the smart kids, you Since you’re the smart kids, you figured out in elementary school to figured out in elementary school to stay behind the bigger kids to keep stay behind the bigger kids to keep from getting hit! The electrons in from getting hit! The electrons in

the the first or second energy level shield first or second energy level shield the outer valence electrons from the the outer valence electrons from the Mother Nucleus’ attractive force. Mother Nucleus’ attractive force.

This puts the atom at a lower This puts the atom at a lower energy energy

state and makes it more stable. state and makes it more stable.

Relate this to ENERGY whenever Relate this to ENERGY whenever possible. possible.

Here we go!Here we go!

Minimize Minimize Electron/Electron Electron/Electron

RepulsionsRepulsions

Atomic RadiusAtomic Radius

No sharp No sharp

boundary boundary beyond beyond

which the which the

electron never electron never strays!strays!!!

Use diatomics and determine radius, Use diatomics and determine radius,

then react with others and then react with others and

determine the radius of others.determine the radius of others.

Radii decreasesRadii decreases ( ()) moving across a moving across a

period AND increases period AND increases (()) moving moving

down a row (family)down a row (family)

The more protons for the same The more protons for the same

number of energy levels—number of energy levels—

increases as we move from left increases as we move from left to to

right across the periodic table.right across the periodic table.

The Effective Nuclear The Effective Nuclear Charge Charge (Z (Zeffeff))

This shrinks the electron cloud This shrinks the electron cloud until…until…

……the point at which electron the point at which electron

repulsions overcome the nuclear repulsions overcome the nuclear

attraction and stop the contraction of attraction and stop the contraction of

electron shells.electron shells.

The principal The principal

level, n, level, n,

determines the determines the

size of an atom size of an atom

——add another add another

level and the level and the

atoms get atoms get MUCH MUCH

larger radii.larger radii.

As we move down a family, the As we move down a family, the

attractive force of the nucleus attractive force of the nucleus

dissipates with increased dissipates with increased distance.distance.

Shielding is only a valid argument Shielding is only a valid argument

when comparing elements from when comparing elements from period period

to period since shielding is incomplete to period since shielding is incomplete

withinwithin a period. a period.

Use this argument with extreme Use this argument with extreme

caution! It should NOT be your caution! It should NOT be your

favorite!favorite!

Ionization EnergyIonization Energy

Energy required to remove an Energy required to remove an

electron from the atom electron from the atom IN THE IN THE

GAS PHASE. GAS PHASE.

Costs EnergyCosts Energy

Removing each subsequent electron Removing each subsequent electron

requires more energy. Second IE, requires more energy. Second IE,

Third IE, etc. Third IE, etc.

A A HUGEHUGE energy price is paid if energy price is paid if the the

subsequent removal of electrons subsequent removal of electrons is is

from another sublevel or, Heaven from another sublevel or, Heaven

forbid, another principal E level forbid, another principal E level

(core). (core).

Some more than others!!Some more than others!!

Increased distance from the Increased distance from the nucleus nucleus

and increased shielding by full and increased shielding by full

principal E levels means it principal E levels means it requires requires

less E to remove an Electron.less E to remove an Electron.

↓↓ Down a FamilyDown a Family

Across a PeriodAcross a Period

due to increasing Zdue to increasing Zeffeff

Let’s talk EXCEPTIONS!!Let’s talk EXCEPTIONS!!

An anomaly occurs at “messing up a An anomaly occurs at “messing up a

half-filled or filled sublevel”. half-filled or filled sublevel”.

There’s nothing magical about this There’s nothing magical about this

and electrons are not “happier” as a and electrons are not “happier” as a

result. result.

The simple truth is that when The simple truth is that when electron electron

pairing first occurs within an orbital, pairing first occurs within an orbital,

there is an increase in there is an increase in

electron/electron repulsions which electron/electron repulsions which

makes it require less energy [easier] makes it require less energy [easier]

to remove an electron; thus the IE to remove an electron; thus the IE

drops.drops.

LOOK AT LOOK AT

Oxygen vs. NitrogenOxygen vs. Nitrogen

It requires less energy to remove an It requires less energy to remove an

electron from oxygen’s valence IN electron from oxygen’s valence IN

SPITE OF AN INCREASING ZSPITE OF AN INCREASING Zeffeff

because oxygen’s pbecause oxygen’s p44 electron is the electron is the

first to pair within the orbital thus first to pair within the orbital thus

experiencing increased repulsion experiencing increased repulsion

which lowers the amount of energy which lowers the amount of energy

required to remove it!required to remove it!

Also, look at the drop in IE from sAlso, look at the drop in IE from s22

to pto p11. This is also IN SPITE OF AN . This is also IN SPITE OF AN

INCREASING ZINCREASING Zeffeff. This drop in . This drop in

energy required is due to the fact energy required is due to the fact

that you are removing a p that you are removing a p electron electron

rather than an s electron.rather than an s electron.

The p’s are less tightly held BECAUSE The p’s are less tightly held BECAUSE

they do not penetrate the electron they do not penetrate the electron

cloud toward the nucleus as well as an cloud toward the nucleus as well as an

s electron. The general trend is that s s electron. The general trend is that s

is held most tightly since it penetrates is held most tightly since it penetrates

more, then p, d and f…more, then p, d and f…

Electron AffinityElectron Affinity

Liking for electronsLiking for electrons

Force feeding an element an Force feeding an element an electronelectron

Energy associated with the addition Energy associated with the addition of of

an electron to a gaseous atom: an electron to a gaseous atom:

X X (g)(g) + e + e-- X X-- (g)(g)

If the addition of an electron is If the addition of an electron is

exothermic, then you’ll see a exothermic, then you’ll see a negative negative

sign on the energy change.sign on the energy change.

The converse is also true. The converse is also true.

The more negative the quantity, The more negative the quantity, the the

more E is released. more E is released.

This matches our sign This matches our sign convention in convention in

thermodynamics.thermodynamics.

↓↓ down a family [that means becomes down a family [that means becomes

less negative a.k.a. more positive, less negative a.k.a. more positive,

giving off less energy]—due to giving off less energy]—due to

increased distance from the nucleus increased distance from the nucleus

with each increasing principal E level. with each increasing principal E level.

The nucleus is farther from the The nucleus is farther from the

valence level and more shielded.valence level and more shielded.

↑↑ across a period [that means across a period [that means

becomes more negative, giving off becomes more negative, giving off

more energy]—Again the increasing more energy]—Again the increasing

ZZeff eff draws in the electron. The draws in the electron. The

interactions of electron repulsions interactions of electron repulsions

wreaks havoc with this wreaks havoc with this generalization generalization

as we shall soon see!as we shall soon see!

Let’s talk EXCEPTIONS!!Let’s talk EXCEPTIONS!!

First, the lines on the diagram First, the lines on the diagram below below

connect adjacent elements. connect adjacent elements.

The absence of a line indicates missing The absence of a line indicates missing elements whose atoms do not add elements whose atoms do not add an electron exothermically and thus an electron exothermically and thus do not form stable isolated anions do not form stable isolated anions [remember these are all –1 ions at [remember these are all –1 ions at this point].this point].

An AnomalyAn Anomaly

No N - yet there is a CNo N - yet there is a C

This is due to their electron This is due to their electron

repulsions compared to their repulsions compared to their

configurations. configurations.

N is pN is p33 while C is p while C is p22. C adds an . C adds an

electron WITHOUT PAIRING and electron WITHOUT PAIRING and

increasing eincreasing e--/e/e-- repulsion and repulsion and

therefore forms a stable ion while N therefore forms a stable ion while N

would have to pair electrons and would have to pair electrons and the the

increased repulsions overcome the increased repulsions overcome the

increasing Zincreasing Zeffeff..

OO2-2- doesn’t exist in isolated form doesn’t exist in isolated form

[gasp] for the same reason. It’s p[gasp] for the same reason. It’s p44, ,

so adding the first electron causes so adding the first electron causes

a subsequent pairing. BUT, it has a a subsequent pairing. BUT, it has a

greater Zgreater Zeffeff than N, so it can form O than N, so it can form O--. .

BUT, adding the second electron BUT, adding the second electron fills fills

the p’s and that increased repulsion the p’s and that increased repulsion

overpowers the Zoverpowers the Zeffeff of oxygen. of oxygen.

Never fear, oxide ions exist in Never fear, oxide ions exist in

plenty of compounds so we haven’t plenty of compounds so we haven’t

exactly been lying to you!exactly been lying to you!

F is weird -- strong eF is weird -- strong e--/e/e-- repulsion repulsion

since the p orbitals are really small since the p orbitals are really small

in the second level, therefore, in the second level, therefore,

repulsions are high. In subsequent repulsions are high. In subsequent

halogen orbitals, it’s not as halogen orbitals, it’s not as

noticeable.noticeable.

Ionic RadiiIonic Radii

CationsCations

shrink big time since the shrink big time since the nucleus is nucleus is

now attracting fewer electronsnow attracting fewer electrons

AnionsAnions

expand since the nucleus is expand since the nucleus is now now

attracting MORE electrons than attracting MORE electrons than

there are protons AND there is there are protons AND there is

enhanced electron/electron enhanced electron/electron

repulsionrepulsion

IsoelectronicIsoelectronic

ions containing the same ions containing the same number of number of

electrons electrons

Consider the # of protons to Consider the # of protons to

determine size. determine size.

Oxide vs. Fluoride.Oxide vs. Fluoride.

Electronegativity (EElectronegativity (Enn))

The ability of an atom IN A The ability of an atom IN A

MOLECULE [meaning it’s MOLECULE [meaning it’s

participating in a BOND] to attract participating in a BOND] to attract

shared electrons to itself. Think shared electrons to itself. Think

““tug of war”. Now you know why tug of war”. Now you know why

they teach you such games in they teach you such games in

elementary school!elementary school!

Linus Pauling’s ScaleLinus Pauling’s Scale

Nobel Prize for Chemistry & Nobel Prize for Chemistry & PeacePeace

Fluorine is the most EFluorine is the most Enn

Francium is the least EFrancium is the least Enn

Why is F the most?Why is F the most?

Highest ZHighest Zeffeff and smallest so that and smallest so that

the nucleus is closest to the the nucleus is closest to the

““action”. action”.

Why is Fr the least?Why is Fr the least?

Lowest ZLowest Zeffeff and largest so that and largest so that the the

nucleus is farthest from the nucleus is farthest from the

““action”.action”.

We’ll use this concept a great We’ll use this concept a great deal deal

in our discussions about bonding in our discussions about bonding

since this atomic trend is since this atomic trend is only only

used when atoms form used when atoms form molecules.molecules.

Exercise 8Exercise 8Trends in Ionization Trends in Ionization EnergiesEnergiesThe first ionization energy for The first ionization energy for

phosphorus is 1060 kJ/mol, and phosphorus is 1060 kJ/mol, and

that for sulfur is 1005 kJ/mol. that for sulfur is 1005 kJ/mol.

Why?Why?

Exercise 9Exercise 9 Ionization Energies Ionization Energies

Consider atoms with the Consider atoms with the following following

electron configurations:electron configurations:

a.a. 1s 1s222s2s222p2p66

b.b. 1s 1s222s2s222p2p663s3s11

c.c. 1s 1s222s2s222p2p663s3s22

Identify each atom. Identify each atom.

Which atom has the largest first Which atom has the largest first ionization energy, and which one ionization energy, and which one has the smallest second has the smallest second

ionization ionization energy? energy?

Explain your choices.Explain your choices.

SolutionSolution

A: Ne; largest IE A: Ne; largest IE

B: Na B: Na

C: Mg; smallest IEC: Mg; smallest IE22

Exercise 10Exercise 10 Trends in Radii Trends in Radii

Predict the trend in radius for the Predict the trend in radius for the

following ions: following ions:

BeBe2+2+ Mg Mg2+2+ Ca Ca2+2+ Sr Sr2+2+

SolutionSolution

BeBe2+2+ < Mg < Mg2+2+ < Ca < Ca2+2+ < Sr < Sr2+2+