Electron Configurations
BOHR’S MODEL-ELECTRON CLOUD Energy level of an
electron• analogous to the
rungs of a ladder The electron
cannot exist between energy levels, just like you can’t stand between rungs on a ladder
A QUANTUM of energy is the amount of energy
required to move an electron from one energy level to another
IN 1926, ERWIN SCHRODINGER derived an
equation that described the energy and position of the electrons in an atom
THE QUANTUM MECHANICAL MODEL
Has energy levels for electrons.
Orbits are not circular. It can only tell us the
probability of finding an electron a certain distance from the nucleus.
THE QUANTUM MECHANICAL MODEL
The atom is found inside a blurry “electron cloud”
An area where there is a chance of finding an electron.
Think of fan blades
ATOMIC ORBITALS• atomic orbitals (coined by scientists in
1932) - regions where there is a high probability of finding an electron.
Sublevels- letters s, p, d, and f
PRINCIPAL QUANTUM NUMBERGenerally symbolized by “n”, it denotes the shell (energy level/period) in which the electron is located.
Maximum number of electrons that can fit in an energy level is: 2n2
SUMMARY
s
p
d
f
# of shapes (orbitals)
Maximum electrons
Starts at energy level
1 2 1
3 6 2
5 10 3
7 14 4
ELECTRON CONFIGURATIONS… …are the way electrons are
arranged in various orbitals around the nuclei of atoms.
THREE RULES TELL US HOW:
1)Aufbau principle - electrons enter the lowest energy first.
2) Pauli Exclusion Principle - at most 2 electrons per orbital - different spins
PAULI EXCLUSION PRINCIPLE
No two electrons in an atom can have the same four quantum numbers.
Wolfgang Pauli
To show the different direction of spin, a pair in the same orbital is written as:
ELECTRON CONFIGURATIONS3) Hund’s Rule- When electrons
occupy orbitals of equal energy, they don’t pair up until they have to.
Let’s write the electron configuration for Phosphorus
The first two electrons go into the 1s orbital
Notice the opposite direction of the spins
only 13 more to go...
Incr
easi
ng e
nerg
y
1s
2s
3s
4s5s6s7s
2p
3p
4p5p6p
3d
4d5d
7p 6d
4f5f
The next electrons go into the 2s orbital
only 11 more...Incr
easi
ng e
nerg
y
1s
2s
3s
4s5s6s7s
2p
3p
4p5p6p
3d
4d5d
7p 6d
4f5f
• The next electrons go into the 2p orbital
• only 5 more...Incr
easi
ng e
nerg
y
1s
2s
3s
4s5s6s7s
2p
3p
4p5p6p
3d
4d5d
7p 6d
4f5f
• The next electrons go into the 3s orbital
• only 3 more...Incr
easi
ng e
nerg
y
1s
2s
3s
4s5s6s7s
2p
3p
4p5p6p
3d
4d5d
7p 6d
4f5f
Incr
easi
ng e
nerg
y
1s
2s
3s
4s5s6s7s
2p
3p
4p5p6p
3d
4d5d
7p 6d
4f5f
• The last three electrons go into the 3p orbitals.
They each go into separate shapes (Hund’s)
• 3 unpaired electrons Orbital
notation
HOWEVER, THERE IS AN EASIER WAY TO DO ELECTRON CONFIGURATIONS Let’s stick with P
= 1s22s22p63s23p3 Confused? Don’t be…there is an easy
way to write these things based on the positions of elements on the chart
First, grab your chart
Look at the Labels
group 1: s1 Group 2: s2 Group 3: p1 Group 4: p2 Group 5: p3 Group 6: p4 Group 7: p5 Group 8: p6 Transition
Metals: d 1-10 Lanthanide
series f: 1-14
Now, go back to P What period is P?
3 What group is P?
5 So, now we build
up: 1s1 (H), 1s2
(He), 2s1 (Li), 2s2 (Be), 2p1 (B), 2p2 (C), 2p3, (N), 2p4 (O), 2p5 (F), 2p6 (Ne), 3s1 (Na), 3s2 (Mg), 3p1 (Al), 3p2 (Si), 3p3 (P)
1s22s22p63s23p3
LET’S TRY THESE TOGETHER H
He
Li
Be
B
C
N
O
F
Ne