Aluminium
Aluminium (Al) is a post-transition metal with atomic number 13 and an atomic mass of 26.982. Its electron configuration is [Ne] 3s2 3p1, which gives it 3 valence electrons.
Aluminium key data
| Symbol | Al |
|---|---|
| Atomic number | 13 |
| Atomic mass (standard atomic weight) | 26.982 |
| Molar mass | 26.982 g/mol |
| Protons | 13 |
| Neutrons (most abundant isotope, aluminium-27) | 14 |
| Electrons (neutral atom) | 13 |
| Valence electrons | 3 |
| Category | Post-transition metal |
| Period | 3 |
| Group | 13 |
| Block | p-block |
| Noble gas notation | [Ne] 3s2 3p1 |
| Full electron configuration | 1s2 2s2 2p6 3s2 3p1 |
| Electrons per shell | 2, 8, 3 |
Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.
The values are facts and free to use; this page’s selection and presentation are © 2026 ScienceQuest.
Measured properties of aluminium
From PubChem, the US National Institutes of Health. Public domain. The discovery year is the year aluminium was first isolated, from Wikipedia’s timeline of chemical element discoveries, in place of PubChem’s “Ancient”.
| Melting point | 933.44 K (660.29 °C), 65th of 103 by melting point |
|---|---|
| Boiling point | 2792 K (2518.9 °C), 47th of 93 by boiling point |
| Density | 2.7 g/cm³, 71st of 96 by density |
| State at room temperature | Solid |
| Electronegativity | 1.61 (Pauling), 49th of 95 by electronegativity |
| Van der Waals radius | 184 pm, 78th of 99 by atomic radius |
| First ionisation energy | 5.986 eV (577.6 kJ/mol), 79th of 102 by first ionisation energy |
| Electron affinity | 0.441 eV (42.6 kJ/mol), 45th of 57 by electron affinity |
| Common oxidation states | +3 |
| Discovered | 1825 |
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.
Aluminium electron configuration
The full electron configuration of aluminium is 1s2 2s2 2p6 3s2 3p1. With the noble-gas core collapsed it is [Ne] 3s2 3p1, and the outermost subshell is 3p1.
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 aluminium 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 = 26.982 / (6.02214076 × 10²³)
- = 4.4805 × 10⁻²³ g
Atoms in one gram
- atoms per gram = 6.02214076 × 10²³ / 26.982
- = 2.2319 × 10²² atoms
Aluminium on the periodic table
Aluminium is in period 3, group 13, in the p-block.
The other elements of group 13 are boron, gallium, indium, thallium and nihonium.