Topic 2: Atomic structure - 2.2 Electron configuration

Nature of science: Developments in scientific research follow improvements in apparatus-the use of electricity and magnetism in Thomson's cathode rays.(1.8) Theories being superseded-quantum mechanics is among the most current models of the atom. (1.9) Use theories to explain natural phenomena-line spectra explained by the Bohr model of the atom. (2.2)


Emission spectra are produced when photons are emitted from atoms as excited electrons return to a lower energy level.

The line emission spectrum of hydrogen provides evidence for the existence of electrons in discrete energy levels, which converge at higher energies

The main energy level or shell is given an integer number, n, and can hold a maximum number of electrons, 2n2.

A more detailed model of the atom describes the division of the main energy level into s, p, d and f sub-levels of successively higher energies.

Sub-levels contain a fixed number of orbitals, regions of space where there is a high probability of finding an electron.

Each orbital has a defined energy state for a given electronic configuration and chemical environment and can hold two electrons of opposite spin..

Applications and skills

Description of the relationship between colour, wavelength, frequency and energy across the electromagnetic spectrum

Distinction between a continuous spectrum and a line spectrum. Description of the emission spectrum of the hydrogen atom, including the relationships between the lines and energy transitions to the first, second and third energy levels.

Recognition of the shape of an s atomic orbital and the px, py and pz atomic orbitals.

Application of the Aufbau principle, Hund's rule and the Pauli exclusion principle to write electron configurations for atoms and ions up to Z = 36.


Details of the electromagnetic spectrum are given in the data booklet in section 3.

The names of the different series in the hydrogen line emission spectrum are not required.

Full electron configurations (eg 1s2 2s2 2p6 3s2 3p4) and condensed electron configurations (eg [Ne] 3s2 3p4) should be covered. Orbital diagrams should be used to represent the character and relative energy of orbitals. Orbital diagrams refer to arrow-in-box diagrams, such as the one given below.

The electron configurations of Cr and Cu as exceptions should be covered.