CHAPTER 1

2

ELECTR

ONS IN A

TOMS

BRODERSEN

HONORS CHEM 2

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4

BOHR’S MODEL

Why don’t the electrons fall into the nucleus?

Move like planets around the sun.In circular orbits at different

levels.Amounts of energy separate one

level from another.

BOHR’S MODEL

Nucleus

Electron

Orbit

Energy Levels

Nucleus

Electron

Orbit

Energy Levels

BOHR POSTULATED THAT:

Fixed energy related to the orbit

Electrons cannot exist between orbits

The higher the energy level, the further it is away from the nucleus

An atom with maximum number of electrons in the outermost orbital energy level is stable (unreactive)

ELECTROMAGNETIC ELECTROMAGNETIC RADIATIONRADIATIONELECTROMAGNETIC ELECTROMAGNETIC RADIATIONRADIATION

ELECTROMAGNETIC RADIATION.

ELECTROMAGNETIC ELECTROMAGNETIC RADIATIONRADIATIONELECTROMAGNETIC ELECTROMAGNETIC RADIATIONRADIATIONMost subatomic particles behave as PARTICLES and obey Most subatomic particles behave as PARTICLES and obey

the physics of waves.the physics of waves.

wavelengthVisible light

wavelength

Ultaviolet radiation

Amplitude

Node

ELECTROMAGNETIC ELECTROMAGNETIC RADIATIONRADIATIONELECTROMAGNETIC ELECTROMAGNETIC RADIATIONRADIATION

Waves have a frequencyWaves have a frequency

Use the Greek letter “nu”, Use the Greek letter “nu”, , for , for frequency, and units are “cycles per frequency, and units are “cycles per sec”sec”

All radiation: All radiation: • • = c = cwhere c = velocity of light = 3.00 x 10where c = velocity of light = 3.00 x 1088 m/secm/sec

ELECTROMAGNETIC ELECTROMAGNETIC RADIATIONRADIATIONELECTROMAGNETIC ELECTROMAGNETIC RADIATIONRADIATION

HOW DID HE DEVELOP HIS THEORY?

• He used mathematics to explain the visible spectrum of hydrogen gas

• http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/linesp16.swf

Radiowaves

Microwaves

Infrared .

Ultra-violet

X-Rays

GammaRays

Low energy

High energy

Low Frequency

High Frequency

Long Wavelength

Short WavelengthVisible Light

THE LINE SPECTRUM

• electricity passed through a gaseous element emits light at a certain wavelength

• Can be seen when passed through a prism

• Every gas has a unique pattern (color)

LINE SPECTRUM OF VARIOUS ELEMENTS

BOHR’S TRIUMPH

His theory helped to explain periodic law

Halogens are so reactive because it has one e- less than a full outer orbital

Alkali metals are also reactive because they have only one e- in outer orbital

ATOMIC LINE EMISSION ATOMIC LINE EMISSION SPECTRA AND NIELS BOHRSPECTRA AND NIELS BOHRATOMIC LINE EMISSION ATOMIC LINE EMISSION SPECTRA AND NIELS BOHRSPECTRA AND NIELS BOHR

Bohr’s greatest contribution Bohr’s greatest contribution to science was in building a to science was in building a simple model of the atom. simple model of the atom. It was based on an It was based on an understanding of theunderstanding of the LINE LINE EMISSION SPECTRAEMISSION SPECTRA of of excited atoms.excited atoms.

Problem is that the model Problem is that the model only works for Honly works for HNiels BohrNiels Bohr

(1885-1962)(1885-1962)

ATOMIC SPECTRAATOMIC SPECTRAATOMIC SPECTRAATOMIC SPECTRA

+Electronorbit

One view of atomic structure in early 20th century was that an One view of atomic structure in early 20th century was that an electron (e-) traveled about the nucleus in an orbit.electron (e-) traveled about the nucleus in an orbit.

ATOMIC SPECTRA AND ATOMIC SPECTRA AND BOHRBOHRATOMIC SPECTRA AND ATOMIC SPECTRA AND BOHRBOHR

Bohr said classical view is Bohr said classical view is wrong. wrong.

Need a new theory — now called Need a new theory — now called QUANTUMQUANTUM or or WAVE WAVE MECHANICSMECHANICS..

e- can only exist in certain e- can only exist in certain discrete orbitsdiscrete orbits

e- is restricted to e- is restricted to QUANTIZEDQUANTIZED energy state (quanta = bundles energy state (quanta = bundles of energy)of energy)

Schrodinger applied idea of e- Schrodinger applied idea of e- behaving as a wave to the behaving as a wave to the problem of electrons in atoms.problem of electrons in atoms.

He developed the He developed the WAVE WAVE EQUATIONEQUATION

Solution gives set of math Solution gives set of math expressions called expressions called WAVE WAVE

FUNCTIONS, FUNCTIONS, Each describes an allowed energy Each describes an allowed energy

state of an e-state of an e-

E. SchrodingerE. Schrodinger1887-19611887-1961

QUANTUM OR WAVE QUANTUM OR WAVE MECHANICSMECHANICSQUANTUM OR WAVE QUANTUM OR WAVE MECHANICSMECHANICS

HEISENBERG HEISENBERG UNCERTAINTY UNCERTAINTY PRINCIPLEPRINCIPLE

Problem of defining nature Problem of defining nature of electrons in atoms of electrons in atoms solved by W. Heisenberg.solved by W. Heisenberg.

Cannot simultaneously Cannot simultaneously define the position and define the position and momentum (= m•v) of an momentum (= m•v) of an electron.electron.

We define e- energy exactly We define e- energy exactly but accept limitation that but accept limitation that we do not know exact we do not know exact position.position.

Problem of defining nature Problem of defining nature of electrons in atoms of electrons in atoms solved by W. Heisenberg.solved by W. Heisenberg.

Cannot simultaneously Cannot simultaneously define the position and define the position and momentum (= m•v) of an momentum (= m•v) of an electron.electron.

We define e- energy exactly We define e- energy exactly but accept limitation that but accept limitation that we do not know exact we do not know exact position.position.

W. HeisenbergW. Heisenberg1901-19761901-1976

ARRANGEMENT OF ARRANGEMENT OF ELECTRONS IN ATOMSELECTRONS IN ATOMSARRANGEMENT OF ARRANGEMENT OF ELECTRONS IN ATOMSELECTRONS IN ATOMSElectrons in atoms are arranged asElectrons in atoms are arranged as

LEVELSLEVELS (n) (n)

SUBLEVELSSUBLEVELS (l) (l)

ORBITALSORBITALS (m (mll))

QUANTUM NUMBERSQUANTUM NUMBERSQUANTUM NUMBERSQUANTUM NUMBERSThe The shape, size, and energyshape, size, and energy of each orbital is a function of 3 quantum of each orbital is a function of 3 quantum

numbers which describe the location of an electron within an atom numbers which describe the location of an electron within an atom or ionor ion

n n (principal)(principal) ---> energy level---> energy level

ll (orbital) (orbital) ---> shape of orbital---> shape of orbital

mmll (magnetic)(magnetic) ---> designates a particular ---> designates a particular suborbitalsuborbital

The fourth quantum number is not derived from the wave functionThe fourth quantum number is not derived from the wave function

ss (spin)(spin) ---> spin of the electron ---> spin of the electron (clockwise or counterclockwise: ½ or – ½)(clockwise or counterclockwise: ½ or – ½)

QUANTUM NUMBERSQUANTUM NUMBERSQUANTUM NUMBERSQUANTUM NUMBERS

So… if two electrons are in the same So… if two electrons are in the same place at the same time, they must be place at the same time, they must be repelling, so at least the spin repelling, so at least the spin quantum number is different!quantum number is different!

The The Pauli Exclusion PrinciplePauli Exclusion Principle says that says that no two electrons within an atom (or no two electrons within an atom (or ion) can have the same four quantum ion) can have the same four quantum numbers.numbers.

If two electrons are in the same energy If two electrons are in the same energy level, the same sublevel, and the level, the same sublevel, and the same orbital, they must repel.same orbital, they must repel.

Think of the 4 quantum numbers as the Think of the 4 quantum numbers as the address of an electron… Country > address of an electron… Country > State > City > StreetState > City > Street

DRAWBACK

• Bohr’s theory did not explain or show the shape or the path traveled by the electrons.

• His theory could only explain hydrogen and not the more complex atoms

ENERGY LEVELS

Further away from the nucleus means more energy.

There is no “in between” energy

Energy Levels

First

Second

Third

Fourth

Fifth

Incr

easi

ng e

nerg

y }

THE QUANTUM MECHANICAL MODELEnergy is quantized. It comes in chunks.

A quanta is the amount of energy needed to move from one energy level to another.

Since the energy of an atom is never “in between” there must be a quantum leap in energy.

Schrödinger derived an equation that described the energy and position of the electrons in an atom

ATOMIC ORBITALS

Principal Quantum Number (n) = the energy level of the electron.

Within each energy level the complex math of Schrödinger's equation describes several shapes.

These are called atomic orbitalsRegions where there is a high

probability of finding an electron

S ORBITALS

1 s orbital for

every energy level

1s 2s 3s

Spherical shaped

Each s orbital can hold 2 electrons

Called the 1s, 2s, 3s, etc.. orbitals

P ORBITALS

Start at the second energy level

3 different directions

3 different shapes

Each orbital can hold 2 electrons

The p Sublevel has 3 p orbitals

THE D SUBLEVEL CONTAINS 5 D ORBITALS• The D sublevel starts in the 3rd energy

level • 5 different shapes (orbitals)• Each orbital can hold 2 electrons

THE F SUBLEVEL HAS 7 F ORBITALS

• The F sublevel starts in the fourth energy level

• The F sublevel has seven different shapes (orbitals)

• 2 electrons per orbital

SUMMARY

s

p

d

f

# of shapes (orbitals)

Max # of electrons

1 2 1

3 6 2

5 10 3

7 14 4

Sublevel

Starts at energy level

ELECTRON CONFIGURATIONS

The way electrons are arranged in atoms.

Aufbau principle- electrons enter the lowest energy first.

This causes difficulties because of the overlap of orbitals of different energies.

Pauli Exclusion Principle- at most 2 electrons per orbital - different spins

ELECTRON CONFIGURATIONS

First Energy Levelonly s sublevel (1 s orbital)only 2 electrons1s2

Second Energy Levels and p sublevels (s and p orbitals are

available)2 in s, 6 in p2s22p6

8 total electrons

Third energy level

s, p, and d orbitals

2 in s, 6 in p, and 10 in d

3s23p63d10

18 total electrons

Fourth energy level

s,p,d, and f orbitals

2 in s, 6 in p, 10 in d, and 14 in f

4s24p64d104f14

32 total electrons

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

ELECTRON CONFIGURATIONHund’s Rule- When electrons occupy orbitals of equal energy they don’t pair up until they have to .

The first to electrons go into the 1s orbital

Notice the opposite spins

only 13 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

The next electrons go into the 2s orbital

only 11 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The next electrons go into the 2p orbital

• only 5 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The next electrons go into the 3s orbital

• only 3 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The last three electrons go into the 3p orbitals.

• They each go into separate shapes

• 3 unpaired electrons

• 1s22s22p63s23p3

ORBITALS FILL IN ORDER Lowest energy to higher energy.

Adding electrons can change the energy of the orbital.

Half filled orbitals have a lower energy.

Makes them more stable.

Changes the filling order

WRITE THESE ELECTRON CONFIGURATIONS

Titanium - 22 electrons

1s2

2s2

2p6

3s2

3p6

4s2

3d2

Vanadium - 23 electrons 1s2

2s2

2p6

3s2

3p6

4s2

3d3

Chromium - 24 electrons

1s2

2s2

2p6

3s2

3p6

4s2

3d4 is expected

But this is wrong!!

CHROMIUM IS ACTUALLY1s

22s

22p

63s

23p

64s

13d

5

Why?

This gives us two half filled orbitals.

Slightly lower in energy.

The same principal applies to copper.

COPPER’S ELECTRON CONFIGURATIONCopper has 29 electrons so we expect

1s2

2s2

2p6

3s2

3p6

4s2

3d9

But the actual configuration is

1s2

2s2

2p6

3s2

3p6

4s1

3d10

This gives one filled orbital and one half filled orbital.

Remember these exceptions

GREAT S

ITE T

O PRACTI

CE

AND INSTA

NTLY

SEE

RESULTS F

OR

ELECTR

ON CONFIG

URATIO

N.

PRACTICE

Time to practice on your own filling up electron configurations.

Do electron configurations for the first 20 elements on the periodic table.