
Shorthand way of writing electron
configuration of atoms
Ne:
10
2
1s
Number of
electrons
2
2s
Energy sublevel
Elemental Symbol and
atomic number
Principal energy level
6
2p

Longhand Configuration
S 16e- 1s2 2s2 2p6 3s2 3p4
Core Electrons
Valence Electrons
Shorthand Configuration
S
16e
[Ne]
2
3s
4
3p
The electrons in the
outermost energy
level.
 s and p electrons in
last shell

Valence Electrons

As (atomic number 33) 5 valence electrons

 1s22s22p63s23p64s23d104p3

Example - Germanium
1
2
3
4
5
6
7
X X X
X X
X X X
X X
X X
X
[Ar]4s2 3d10 4p2
Let’s Practice
 P (atomic number 15)
 1s22s22p63s23p3

Ca
(atomic number 20)

As
(atomic number 33)

 1s22s22p63s23p64s2
 1s22s22p63s23p64s23d104p3
Noble Gas Configuration
[Ne] 3s23p3
[Ar] 4s2
[Ar] 4s23d104p3
W (atomic number 74)
 1s22s22p63s23p64s23d104p65s24d105p66s24f145d4
[Xe] 6s24f145d4
Energy Sublevels
• Labeled s, p, d, or f
– Based on shape of the atom’s orbitals
Your Turn
 N (atomic number 7)
 1s22s22p3

Na
(atomic number 11)
 1s22s22p63s1

Noble Gas
Configuration
[He] 2s22p3
[Ne] 3s1
Sb (atomic number 51)
 1s22s22p63s23p64s23d104p65s24d105p3

Cr
(atomic number 24)
 1s22s22p63s23p64s23d4
[Kr]5s24d105p3
[Ar] 4s23d4
Why are d and f orbitals always in
lower energy levels?
• d and f orbitals require LARGEamounts of energy
• It’s better (lower in energy) to skip a sublevel
that requires a large amount of energy (d and f
orbtials) for one in a higher level but lower energy
This is the reason for the diagonal rule!
BE SURE TO FOLLOW THE ARROWS
IN ORDER!



Full energy level
Full sublevel
Half full sublevel
1
2
3
4
5
6
7


Copper
 Expect: [Ar] 4s2 3d9
 Actual: [Ar] 4s1 3d10
Silver
 Expect: [Kr] 5s2 4d9
 Actual: [Kr] 5s1 4d10

Chromium

Molybdenum
 Expect: [Ar] 4s2 3d4
 Actual: [Ar] 4s1 3d5
 Expect: [Kr] 5s2 4d4
 Actual: [Kr] 5s1 4d5
Exceptions are
explained, but not
predicted!
Atoms are more
stable with half full
sublevel


Atoms create stability by losing, gaining or
sharing electrons to obtain a full octet
Isoelectronic with noble gases
+1
1
2
3
4
5
6
7
0
+2
+3 +4 -3 -2 -1
Atoms take electron configuration of the closest
noble gas

Na (atomic number 11)
 1s22s22p63s1
 1s22s22p6 = [Ne]
1
2
3 Na
4
5
6
7
1 Valence electron
Metal = Loses
Ne

P-3 (atomic number 15)
 1s22s22p63s23p6

Ca+2 (atomic number 20)
 1s22s22p63s23p6

Zn+2 (atomic number 30)
Full Octet
 1s22s22p63s23p63d10
 Last valence electrons (s and p)