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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)
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