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