Electron Configuration, Aufbau, Pauli, and Hund's Rules

Arrangement of electrons

The arrangement of electrons around the nucleus, especially the outermost electrons, mainly determines the properties of an element.

Exact location of electrons

Only their probable regions can be described; the exact location cannot be determined.

Bohr's description of electrons

Electrons are described as moving in definite paths or orbits around the nucleus.

Order of filling energy sublevels

Electrons fill energy sublevels from the nearest to the farthest from the nucleus.

Filling before p-sublevel

The s-sublevel must be filled before a p-sublevel is occupied.

Filling before d-sublevel

The p-sublevel must be filled before a d-sublevel is filled.

Energy of sublevels

As the main energy level increases, sublevels have higher energy.

Correct order of filling sublevels

1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, and so on.

Aufbau Principle

Electrons occupy the lowest energy orbital available first.

Aufbau diagram

A tool that helps remember the filling order of orbitals, also known as the diagonal rule.

Electron configuration of Helium

1s².

Electron configuration of Phosphorus

1s² 2s² 2p⁶ 3s² 3p³.

Pauli Exclusion Principle

Only two electrons can occupy an orbital, and they must have opposite spins.

Electron spin in orbital diagrams

Electron spin is shown by vertical arrows in opposite directions (↑↓).

Spin property

A quantum property of electrons, which can be clockwise or counterclockwise.

Hund's Rule

Electrons fill orbitals of equal energy singly first with parallel spins, then pair up.

Reason for separate orbitals

Electrons occupy separate orbitals first to minimize repulsion and maintain stability.

Definition of electron configuration

The way electrons are arranged around the nucleus in successive sublevels and orbitals.

Electron configuration representation

Can also be shown by orbital diagrams with arrows showing electron spins.