Post-transition metalElement 13 · p-block

Aluminum (Al)

Aluminum (Al), also spelled aluminium, is a post-transition metal with atomic number 13 and a standard atomic weight of 26.982. At room temperature it is a solid that melts at 660 °C and boils at 2,519 °C.

13AlAluminum26.982

Atomic number

protons

Atomic weight

26.982

CIAAW 2024

Melting point

660 °C

933.47 K

Boiling point

2,519 °C

2,792.15 K

Density

2.7 g/cm³

near room temperature

Electronegativity

1.61

Pauling scale

State at 25 °C

Solid

Discovered

1825

Denmark

Aluminum at a glance

Identity

Symbol	Al
Atomic number (Z)	13
Atomic weight	26.982 ± 0.001 (CIAAW 2024)
Category	Post-transition metal
Group	13 — boron group
Period	3
Block	p-block
CAS number	7429-90-5

Atomic properties

Electron configuration	[Ne] 3s² 3p¹ Full: 1s² 2s² 2p⁶ 3s² 3p¹
Electrons per shell	2, 8, 3
Oxidation states	+3 Less common: -2, -1, 0, +1, +2
Electronegativity (Pauling)	1.61
First ionisation energy	5.986 eV (577.5 kJ/mol) 2nd: 18.828 eV · 3rd: 28.448 eV
Electron affinity	0.433 eV
Atomic radius (empirical)	125 pm
Covalent radius	126 pm
Van der Waals radius	184 pm

Physical properties

State at 25 °C	Solid
Melting point	660.3 °C · 1,220.6 °F · 933.47 K
Boiling point	2,519 °C · 4,566.2 °F · 2,792.15 K
Density	2.7 g/cm³
Specific heat capacity	0.897 J/(g·K)
Thermal conductivity	237 W/(m·K)
Crystal structure	Face-centred cubic

Isotopes & abundance

Natural occurrence	Primordial
Radioactive	No
Natural isotopes (abundance)	²⁷Al 100%
Stable isotopes	2
Known isotopes	23
Abundance in Earth's crust	82,300 mg/kg
Abundance in seawater	0.002 mg/L

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Aluminum electron configuration

Aluminum has 13 electrons. Written in short form, its ground-state configuration is [Ne] 3s² 3p¹ — the electrons of the noble gas neon, plus 3s² 3p¹.Written out in full: 1s² 2s² 2p⁶ 3s² 3p¹.

As a member of group 13 it has 3 valence electrons in its outer shell (shell 3), which largely decide its chemistry.

3s↑↓

3p↑

Discovery and name

Discovered

1825 — Hans Christian Ørsted (purer metal: Friedrich Wöhler, 1827) · Denmark.

Name

Latin alumen, alum.

Known for

The most abundant metal in Earth's crust. Light and corrosion-resistant, it is used for cans, foil, window frames, aircraft and power lines.

Isotopes of aluminum

Naturally occurring aluminum is a mix of 1 isotope. Each has 13 protons; they differ in the number of neutrons:

Isotope	Protons	Neutrons	Natural abundance	Stability
²⁷Al	13	14	100%	stable

23 isotopes of aluminum are known in our data set (half-lives as published in nuclear data tables).

Aluminum compared with group 13

The other elements in group 13 (boron group), from top to bottom of the table:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Boron	5	10.81	2,077 °C	4,000 °C	2.34 g/cm³	2.04
Aluminum	13	26.982	660 °C	2,519 °C	2.7 g/cm³	1.61
Gallium	31	69.723	30 °C	2,229 °C	5.91 g/cm³	1.81
Indium	49	114.82	157 °C	2,027 °C	7.31 g/cm³	1.78
Thallium	81	204.38	304 °C	1,473 °C	11.8 g/cm³	1.62
Nihonium	113	[286]	—	—	16 g/cm³ (pred.)	—

Frequently asked questions

6 answers

What is the atomic mass of aluminum?

The standard atomic weight of aluminum is 26.982 ± 0.001 (CIAAW 2024), so one mole weighs about 26.982 grams.

How many protons, neutrons and electrons does aluminum have?

A neutral aluminum atom has 13 protons and 13 electrons. Its most common isotope, aluminum-27, has 14 neutrons.

What is the electron configuration of aluminum?

[Ne] 3s² 3p¹ (in full: 1s² 2s² 2p⁶ 3s² 3p¹).

What are the melting and boiling points of aluminum?

Aluminum melts at 660.32 °C (1,220.6 °F) and boils at 2,519 °C (4,566.2 °F).

Is aluminum a metal?

Aluminum is a metal. It is in group 13, period 3, and is a solid at room temperature.

Who discovered aluminum?

1825 — Hans Christian Ørsted (purer metal: Friedrich Wöhler, 1827) (Denmark).