Electron Configuration

H & CP ChemistryChapter 13

Quantum Mechanical Quantum Mechanical Model (Model (better than the better than the

Bohr Model)Bohr Model) Bohr model

describes electrons “in orbit” at different levels around the nucleus. Each level holds 2-8-8-18… electrons.

Quantum model describes each individual electron in a specific configuration based on its energy.

What are electron configurations?What are electron configurations?

Electron Configurations regions of space where electrons are likely to be found, based on their energy.

United States of United States of AmericaAmerica

An electron configuration An electron configuration expresses:expresses:

energy level or shell (the farther it is from the nucleus the more energy it has). A number 1 – 7.

11

22

33

44

Electron energy Electron energy levels or shellslevels or shells

Shell number = Period number

An electron configuration An electron configuration expresses:expresses:

energy level or shell (the farther it is from the nucleus the more energy it has). A number 1 – 7.

sublevel or subshell (shape of the region of space the electron occupies). A letter s, p, d or f.

Subshell or Sublevel - designated by s, p,d,f - refers to the shape(s) of the area in which the electron can be located. - also designates an energy sublevel within the shell. - relative energy: s < p < d < f

s subshell: spherical1 orbital

p subshell: pair of lobes

x y z

x

y

z

d subshell f subshell

1

2

3

4

5

6

7

6

7

1A

2A

3B 4B 5B 6B 7B 8B 8B 8B 1B 2B

3A 4A 5A 6A 7A

8Agroup # = # valence (outside) e-

d p

f

s

Row =# shells

An electron configuration An electron configuration expresses:expresses:

energy level or shell (the farther it is from the nucleus the more energy it has). A number 1 – 7.

sublevel or subshell (shape of the region of space the electron occupies). A letter s, p, d or f.

orbital (specific region within the sublevel). Each orbital has room for up to 2 electrons.

Orbital• refers to the specific area in which the electron can be located within a sublevel• have equal relative energy within a sublevel

s subshell: spherical

1 orbitalp subshell: pair of lobes 3 orbitals

x y z

x

y

z

d subshell

5 orbitalsf subshell

7 orbitals

An electron configuration An electron configuration expresses:expresses:

energy level or shell (the farther it is from the nucleus the more energy it has). A number 1 – 7.

sublevel or subshell (shape of the region of space the electron occupies). A letter s, p, d or f.

orbital (specific region within the sublevel). Each orbital has room for up to 2 electrons.

direction the electron is spinning. Up or down.

How are electron How are electron configurations configurations

expressed?expressed?

Electron configs can be:Written Drawn

Written Electron Written Electron ConfigurationsConfigurations

1s2Energy Energy LevelLevel

SublevelSublevel

Number of Number of electrons in electrons in the sublevelthe sublevel

1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s22 3d 3d1010 4p 4p66 5s 5s22 4d 4d1010 5p 5p66 6s 6s22 4f4f1414… … etc.etc.

Drawn Electron Drawn Electron configurationconfiguration

Drawn in order of increasing energy from bottom to top

Energy level (number) and sublevel (letter) are written

Boxes or lines represent orbitals

represent electrons

Aufbau PrincipleAufbau Principle Aufbau

Principle: Electrons enter orbitals of lowest energy first,

Be careful sometimes energy sublevels in the one energy level can overlap with the next energy level.

represent electrons

LithiumLithiumLithiumLithium

Atomic number = 3

1s22s1 ---> 3 total e-

Group 1A

1s

2s

3s3p

2p

Aufbau Diagram for Li

Hunds RuleHunds Rule When electrons

occupy orbitals of equal energy, 1 electron enters each orbital until all orbitals are filled

Fill out for Nitrogen – has 7 electrons!

CarbonCarbonCarbonCarbon

Group 4AGroup 4A

Atomic number = 6Atomic number = 6

1s1s2 2 2s2s2 2 2p2p22 ---> 6 total e ---> 6 total e--

1s

2s

3s3p

2p

Pauli Exclusion Pauli Exclusion PrinciplePrinciple

To occupy the same orbital electrons must spin in opposite directions

1s

2s

3s3p

2p

SummarySummary

s

p

d

f

# of Orbitals(shapes)

Max # of Electrons in the

Sublevel

Starts at energy level

1 2 1

3 6 2

5 10 3

7 14 4

Sublevel letter

Electronic Configuration according to Quantum Mechanics

The location of an electron is described by 3 terms.

1st Term: Shell (n)

n = 1

n = 2

n = 3

lone electronof Hydrogen So we write 1s1

The Electronic Configuration of Helium He: Atomic # of 2, 2 electrons in a neutral He atom

H 1s1

He 1s2

He 1s

1s

**if there are 2 electrons in the same orbitalthey must have the opposite spin. (Pauli’s Exclusion Principle)

1s

The Electronic Configuration of Lithium (Li)Li: Z=3 Li has 3 electrons.

2nd shell (2)

1s

The Electronic Configuration of Boron & Carbon

2nd shell

2s2p

1s

2nd shell

2s2p

2p 2s

B 1s

C = 1s22s22p2

2p 2s

C 1s

sourcessources www.cast.uark.edu/.../USpop1990.html

http://www.ccs.k12.in.us/chsBS/kons/kons/images/carbon.gif

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch6/quantum.html

http://commons.wikimedia.org/wiki/File:F_orbital.png

http://www.uh.edu/engines/heliumatom.jpg

http://grandinetti.org/Teaching/Chem121/Lectures/MultiElectronAtoms/assets/OrbitalEnergies.gif

http://en.wikipedia.org/wiki/Exposure_(photography)