Structure 1.3 – Electronic configurations

S1.3.3, S1.3.4 & S1.3.5 – Electronic configuration

šŸ“Œ Electronic configuration

  • Electronic configuration shows how electrons are arranged in an atom
  • Electrons occupy energy levels around the nucleus
  • Energy levels are divided into sublevels and orbitals

šŸ“Œ Energy levels and sublevels

  • Energy levels are numbered 1, 2, 3, and 4
  • Each energy level contains sublevels
  • Sublevels are labelled s, p, d, and f
SublevelNumber of orbitalsMaximum electrons
s12
p36
d510

šŸ“Œ Order of filling

1s ā†’ 2s ā†’ 2p ā†’ 3s ā†’ 3p ā†’ 4s ā†’ 3d

šŸ“Œ Rules for filling orbitals

  • Each orbital holds a maximum of two electrons
  • Orbitals of lower energy fill first – Aufbau principle
  • Electrons in the same orbital have opposite spins – Pauli’s exclusion principle
  • Orbitals of equal energy fill singly before pairing – Hund’s rule

EXAMPLE

Oxygen has 8 electrons, 2 in 1s 2 in 2s and 4 in 2p

1s orbital : ā†‘ā†“ (lowest orbital first fills with two oppositely spinning electrons)

2s orbital : ā†‘ā†“ (next orbtial fills with two more oppositely spinning electrons)

2p orbital: ā†‘ā†“ ā†‘ ā†‘ (p orbital singly fills with 3 same spinning electrons and one oppositely spinning one after being fully singly filled)

therefore the electronic configuration of oxygen is 1sĀ² 2sĀ² 2pā“