Electron Configuration and Orbital Notation

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁹

All orbitals of equal energy are occupied by one electron before any single orbital is occupied by a second electron.

Electrons occupy the lowest energy orbitals first before filling higher energy orbitals.

No two electrons in an atom can have the same set of four quantum numbers.

A graphical representation of the arrangement of electrons in an atom's orbitals.

Electrons in the same orbital must have opposite spins, represented by arrows pointing in opposite directions.

The 4s orbital is filled before the 3d orbital due to its lower energy level in the Aufbau principle.

Two electrons, with opposite spins.

Core notation uses the nearest noble gas to simplify the electron configuration.

Copper (Cu) has an electron configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁹, which is an exception.