Atomic Structure

Electron Configurations

• The way electrons are arranged around the nucleus

Standard Notation of Fluorine

Main Energy

Level

Numbers

1, 2, 2Sublevels

Number of electrons in the sub level 2,2,5

1s2 2s2 2p5

Electron Configuration • Energy level of an electron is the region around the

nucleus where it is likely to be moving– N = 1, 2, 3 ,4

• Within each energy level are sub-levels– s, p, d and f

• Each sub-level corresponds to a different cloud shape or atomic orbital

• Atomic orbital is a region where there is a high probability of finding an electron

• Each type of orbital has a unique shape:– s orbitals have a spherical shape (1 orbital)– p orbitals have a dumbbell shape (3 orbitals)– d and f orbitals have more complex shapes (5 orbitals, 7 orbitals)

Electron Configurations

• Lowest energy level (n=1) has only 1 sub-level:– 1s

• Second energy level (n=2) has 2 sub-levels:– 2s and 2p

• Third energy level (n=3) has 3 sublevels:– 3s, 3p and 3d

• Fourth energy level (n=4) has 4 sub-levels:– 4s, 4p, 4d and 4f

Electron Configurations

• How electrons fill the orbitals is based on 3 rules:– The Aufbau principle– The Pauli Exclusion principle– Hund’s rule

Orbital Diagram

Electron Configurations

• The Pauli exclusion principle– Atomic orbital may describe at most 2 electrons

– Electrons must have opposite spins– ↑↓

Electron Configurations

• Hund’s rule• In a set of orbitals, the electrons will fill the

orbitals in a way that would give the maximum number of parallel spins (maximum number of unpaired electrons)

• ↑ ↑ ↑

• Analogy: Students could fill each seat of a school bus, one person at a time, before doubling up.

Orbital Diagram for Hydrogen

1s1

OrbitalDiagram for

Helium1s2

Orbital Diagram for

Lithium1s22s1

Orbital Diagram for

Beryllium1s22s2

Orbital Diagram for

Boron1s22s22p1

OrbitalDiagram for

Carbon1s22s22p2

Orbital Diagram for

Nitrogen1s22s22p3

Standard Notation of Fluorine

Main Energy

Level

Numbers

1, 2, 2Sublevels

Number of electrons in the sub level 2,2,5

1s2 2s2 2p5

Electron Configurations

Electron Configurations

Electron Configurations

• What is the electron configuration for?– Hydrogen

– Lithium

– Fluorine

Electron Configurations – Sodium

– Sulphur

– Rubidium

– Complete the following worksheets – Electron Configurations Level 1– Electron Configurations Level 2– Electron Configurations Worksheet 4