ELECTRON CONFIGURATION
Section 5.2
Stability
Lowest possible energy
Energy levels
The maximum number of electrons in the principle energy level (shell) is 2n2.Energy Level (n)
Maximum # of e-
1 2
2 8
3 18
4 32
Electron Configuration
The Electron Configuration tells us how many electrons exist in each principal energy level (n=1-7) Atomic Number-6 Mass Number- 12
6 protons 6 neutrons 6 electrons Electron Configuration- 2-4
Electron Configuration
The electron configuration for the ground state of an atom is given on the Periodic Table of the Elements.
39.0983 +1
K192-8-8-1
Electron Configuration
What is the electron configuration of a sulfur atom in the ground state?
(1) 2-4(2) 2-6(3) 2-8-4(4) 2-8-6
Three Rules
Aufbau principle Pauli exclusion principle Hund’s rule
Aufbau Principle
Electrons occupy the orbital of lowest energy first.
Orbitals
spdf- comes from a now-discredited system of categorizing spectral lines
s- “strong” p- “principal” d- “diffuse” f- “fundamental”
s orbital
spherical
p orbitals
Dumb bell shaped
d orbitals
Double dumb bell shaped
f orbitals
Very complicated Rare earth elements
Energy levels sublevels orbitals
Principal Energy Level
Number of sublevels
Type of sublevel
n=1 1 1s (1 orbital)
n=2 2 2s (1), 2p (3)
n=3 3 3s (1), 3p (3), 3d (5)
n=4 4 4s(1), 4p (3), 4d (5),
4f (7)
Orbitals- Number of electrons
s-1 orbital= 2 e-
p-3 orbitals= 6 e-
d-5 orbitals= 10 e-
f-7 orbitals= 14 e-
Filling Orbitals
1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f (5g)6s 6p 6d (6f 6g 6h)7s 7p (7d 7f 7g 7h 7i)
Pauli Exclusion Principle
An atomic orbital may describe at most 2 electrons.
Those two electrons must have opposite spins
Spin: a quantum mechanical property of electrons (clockwise/counterclockwise)
Hund’s Rule
Electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible.
Exceptions
Some actual electron configurations differ from those assigned using the Aufbau principle
This leads to variation in chemical behavior
Valence Electrons
Outermost electrons Participate in reactions
Properties of elements Coincides with groups on the Periodic Table
Kernel
The nucleus and inner electrons 2 valence
e-
KERNEL
What is the total number of valence electrons in an atom of electron configuration X?
Which electron configuration represents the excited state of a calcium atom?
Element Electron Configuration
X 2-8-8-2
Y 2-8-7-3
Z 2-8-8
2
2-8-7-3
What is the total number of electrons in the valence shell of an atom of aluminum in the ground state?
(1)8(2)2(3)3(4)10
Lewis Dot Structures
Diagrams that show valence electrons as dots
Lewis (Electron) Dot Structures
C
Your Turn
Draw the Lewis Dot Structures for the following elements: Hg, Mn, K, Au, Cs