Electron Configurations The way electrons are arranged around the nucleus
Standard Notation of Fluorine Main Energy Level Numbers 1, 2, 2 Sublevels Number of electrons in the sub level 2,2,5 1s 2 2s 2 2p 5
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
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.