Electron Configuration
Shorthand way of writing electron configuration of atoms
10Ne: 1s2 2s2 2p6
Elemental Symbol and atomic number
Principal energy level
Energy sublevel
Number of electrons
Shorthand Configuration
S 16e-
Valence Electrons
Core Electrons
S 16e- [Ne] 3s2 3p4
1s22s22p63s23p4
Longhand Configuration
Valence Electrons
As (atomic number 33) 1s22s22p63s23p64s23d104p3
The electrons in the outermost energy level.
s and p electrons in last shell
5 valence electrons
[Ar]4s23d104p2
Example - Germanium
X X X X X X X X X X X X X
Let’s Practice P (atomic number 15)
1s22s22p63s23p3
Ca (atomic number 20) 1s22s22p63s23p64s2
As (atomic number 33) 1s22s22p63s23p64s23d104p3
W (atomic number 74) 1s22s22p63s23p64s23d104p65s24d105p66s24f145d4
Noble Gas Configuration
[Ne] 3s23p3
[Ar] 4s2
[Ar] 4s23d104p3
[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
Sb (atomic number 51)
1s22s22p63s23p64s23d104p65s24d105p3
Cr (atomic number 24)
1s22s22p63s23p64s23d4
Noble GasConfiguration
[He] 2s22p3
[Ne] 3s1
[Kr]5s24d105p3
[Ar] 4s23d4
Why are d and f orbitals always in lower energy levels?
• d and f orbitals require amounts of energy
• It’s better (lower in energy) to 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!
LARGEskip a sublevel
BE SURE TO FOLLOW THE ARROWS IN ORDER!
Full energy levelFull sublevelHalf 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 Expect: [Ar] 4s2 3d4
Actual: [Ar] 4s1 3d5
Molybdenum 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
2
3
4 5
6
7
+1 +
2-3 -2 -1
0
+3
+4
Atoms take electron configuration of the closest noble gas
Na (atomic number 11) 1s22s22p63s1
1s22s22p6 = [Ne]1
2
3
4 5
6
7
Na
1 Valence electronMetal = Loses
Ne
P-3 (atomic number 15)
1s22s22p63s23p6
Ca+2 (atomic number 20)
1s22s22p63s23p6
Zn+2 (atomic number 30)
1s22s22p63s23p63d10
Last valence electrons (s and p)
Full Octet