Blocks in the Periodic Table

Electron Configuration

H. Chemistry

Electron Configuration

The way electrons are arranged around the nucleus.

Quantum Mechanical Model1920’sWerner Heisenberg (Uncertainty Principle)Louis de Broglie (electron has wave properties)Erwin Schrodinger (mathematical equations using probability, quantum numbers)

Principal Quantum Number, nIndicates main energy levels

n = 1, 2, 3, 4…

Each main energy level has sub-levels

Energy Sublevels

s p d f

Angular Momentum Quantum Number , ℓ

Indicates number of sub levels

ℓ = 0 to n-1

ℓ sublevel0 s1 p2 d3 f4 g

Magnetic Quantum Number, mIndicates shape of the orbital sub levels

m = -ℓ ≥ 0 ≥ +ℓ

s subshell: spherical1 orbital

p subshell: pair of lobes

x y z

x

y

z

ℓ=0, m=0

ℓ=1, m = -1 m =0 m =+1

OrbitalThe space where there is a high probability that it is occupied by a pair of electrons.Orbitals are solutions of Schrodinger’s wave equations.

Orbitals in Sublevels

Sublevel # Orbitals # electronss 1 2p 3 6d 5 10f 7 14g 9 18

Three rules are used to build the electron configuration:

Aufbau principlePauli Exclusion PrincipleHund’s Rule

Aufbau Principle

Electrons occupy open orbitals of lowest energy first.

-Pauli Exclusion Principle(Wolfgang Pauli, Austria, 1900-1958)-Electron Spin Quantum Number

An orbital can hold only two electrons and they must have opposite spin.

Electron Spin Quantum Number (ms):

+1/2, -1/2

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.

Recall that electrons repel each other so they try NOT to be paired.

Notations of Electron ConfigurationsStandardShorthand

Standard Notation

of Fluorine

Main Energy Level Numbers 1, 2, 2

Sublevels

Number of electronsin the sub level 2,2,5

1s2 2s2 2p5

Shorthand NotationUse the last noble gas that is located in the periodic table right before the element.Write the symbol of the noble gas in brackets.Write the remaining configuration after the brackets.Ex: Fluorine: [He] 2s2 2p5