Gallium

Gallium (Ga) is a post-transition metal with atomic number 31 and an atomic mass of 69.723. Its electron configuration is [Ar] 3d10 4s2 4p1, which gives it 3 valence electrons.

Gallium key data

Symbol	Ga
Atomic number	31
Atomic mass (standard atomic weight)	69.723
Molar mass	69.723 g/mol
Protons	31
Neutrons (most abundant isotope, gallium-69)	38
Electrons (neutral atom)	31
Valence electrons	3
Category	Post-transition metal
Period	4
Group	13
Block	p-block
Noble gas notation	[Ar] 3d10 4s2 4p1
Full electron configuration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p1
Electrons per shell	2, 8, 18, 3

Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.

Measured properties of gallium

From PubChem, the US National Institutes of Health. Public domain.

Melting point	302.91 K (29.76 °C), 88th of 103 by melting point
Boiling point	2477 K (2203.9 °C), 49th of 93 by boiling point
Density	5.91 g/cm³, 59th of 96 by density
State at room temperature	Solid
Electronegativity	1.81 (Pauling), 42nd of 95 by electronegativity
Van der Waals radius	187 pm, joint 74th of 99 by atomic radius
First ionisation energy	5.999 eV (578.8 kJ/mol), 77th of 102 by first ionisation energy
Electron affinity	0.3 eV (28.9 kJ/mol), 52nd of 57 by electron affinity
Common oxidation states	+3
Discovered	1875

Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.

Gallium electron configuration

The full electron configuration of gallium is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p1. With the noble-gas core collapsed it is [Ar] 3d10 4s2 4p1, and the outermost subshell is 4p1.

Bohr model of gallium (Ga): a nucleus and four shells holding 2, 8, 18 and 3 electrons from the inside out. — Bohr model of gallium (Ga). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Orbital box diagram of gallium (Ga), 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p1: one box per orbital, filled by Hund’s rule, showing one unpaired electron, in 4p. — Orbital diagram of gallium (Ga). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one gallium atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

one atom = 69.723 / (6.02214076 × 10²³)
= 1.1578 × 10⁻²² g

Atoms in one gram

atoms per gram = 6.02214076 × 10²³ / 69.723
= 8.6372 × 10²¹ atoms

Gallium on the periodic table

Gallium is in period 4, group 13, in the p-block.

The other elements of group 13 are boron, aluminium, indium, thallium and nihonium.