Electron Configurations

Electron ConfigurationElectron configuration refer to the arrangement of

electrons within an atom

Because low-energy systems are more stable, electrons are found most

often in a ground state configuration.

Neon (10)

Aufbau PrincipleThe aufbau (off-bow) principle states that electrons

fill the lowest energy orbital available before occupying higher levels.

All orbitals related to an energy sublevel are of

equal energy.

All three 2p orbitals are of equal energy

Aufbau PrincipleAll orbitals related to an energy sublevel are of

equal energy.

All three 2p orbitals are of equal energy

Example

Aufbau PrincipleIn a multi-electron atom, the energy sublevels within

a principal energy level have different energies.

The three 2p orbitals are of higher energy than the

2s orbital.

Example

Aufbau PrincipleEnergy sublevels are filled from lower energy levels to

higher levels, generally following the sequence of s, p, d, and f. However, energy sublevels from different principal

energy levels can overlap.

Example

The 4s sublevel has a lower energy level than

the five 3d orbitals

Aufbau Principle1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p

Aufbau Principle1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p

Pauli Exclusion PrincipleEach electron in an atom has an associated spin, but the

electron is only able to spin in only one of two directions.

One direction Second direction

A maximum of only two electrons can occupy any orbital, but only if they have opposite spins.

Hund’s RuleSingle electrons with the same spin must occupy each

equal energy sublevel orbital before electrons with opposite spins can occupy the same orbital

Each orbital must get one electron before any orbital can get a second electron

p Orbitals

Orbital DiagramsOne method of representing an atom’s electron

configuration is using orbital diagrams.

Unoccupied Orbital

One Electron Full Orbital

Orbital DiagramsFluorine (9)

1s 2s 2pPhosphorus (15)

1s 2s 3s2p 3p

Electron Configuration NotationAnother method for representing electron

configurations is called electron configuration notation and uses superscripts to denote the

number of electrons in each sublevel.

Chlorine (17)

1s2 2s2 2p6 3s2 3p5

Calcium (20)

1s2 2s2 2p6 3s2 3p6 4s2

Noble-Gas NotationA third method uses brackets around the chemical symbol

for the prior noble gas to the element, followed by the rest of the sublevels and superscript electrons.

Sodium (11)[Ne] 3s1

Bromine (35)[Ar] 4s2 3d10 4p5

Iodine (53)[Kr] 5s2 5d10 5p5

Valence ElectronsValence electrons are the electrons in the outermost

principal energy level

Sodium (11)[Ne] 3s1

Bromine (35)[Ar] 4s2 3d10 4p5

Iodine (53)[Kr] 5s2 4d10 5p5

1 valence electron 7 valence electrons

7 valence electrons

Electron Dot StructuresBecause the valence electrons are the only ones involved in forming chemical bonds, a chemist named G.N. Lewis

came up with a visual way to represent the valence electrons called electron dot structures, also called

Lewis dot structures.

PPhosphorus (15)1s2 2s2 2p6 3s2 3p3

The End