Chemical element · reference page

13Al

Aluminium

Aluminium is element 13 (Al), located in period 3, group 13 and the p block. At room temperature its reference phase is solid. Its electron configuration is [Ne] 3s2 3p1.

Atomic number13

Standard atomic weight26.9815384(3)

Group13

Period3

Blockp

Electron configuration[Ne] 3s2 3p1

Electronic structure

What controls its chemistry

Atoms in group 13 have three valence electrons in the outer s and p subshells. The balance between covalent bonding and positive oxidation states changes down the group as atomic size and metallic character increase.

Aluminium is therefore best understood by comparing it with the elements immediately above and below it rather than by treating group 13 as chemically uniform.

Chemical forms

Compounds, ions and materials

Group 13 chemistry includes oxides, halides and covalent or ionic compounds in positive oxidation states. The lighter elements show more covalent character, while the heavier members become progressively more metallic.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 2.7 g/cm³. The melting point is 933.5 K (660.3 °C). The boiling point is 2 743 K (2 470 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where aluminium is found and used

In practice, aluminium is encountered in packaging, aerospace and power lines.

In practice

Examples of real uses

Packaging

Aluminium is used in packaging materials because of low mass, barrier properties, corrosion resistance or ease of forming.

Aerospace

Aluminium is used where low mass, strength, heat resistance or specialised electronic and optical properties matter.

Power lines

Aluminium is used in electrical conductors and power systems because of its combination of conductivity, mass and mechanical properties.

Periodic position

What its neighbours tell us

Aluminium is in period 3 and group 13. In the neighbourhood shown here, silicon is immediately to its right in the same period; boron is above it and gallium below it in the same group. These positions make it possible to compare atomic size, ionisation energy and bonding behaviour with nearby elements.

Reference data

Physical and atomic properties

Classificationpost-transition metal

Phase at room temperatureSolid

Electron shells2 · 8 · 3

Density2.7 g/cm³

Melting point933.5 K (660.3 °C)

Boiling point2 743 K (2 470 °C)

Pauling electronegativity1.61

First ionisation energy577.5 kJ/mol

Electron affinity41.76 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The element’s identification developed through mineral analysis, chemical separation and improvements in atomic theory. Modern identification relies on atomic number rather than on appearance alone.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is 26.9815384(3). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Aluminium has at least one stable isotope. Different isotopes have the same number of protons and therefore the same element identity, but different neutron numbers and atomic masses.

Safety

Handling and exposure

The hazards associated with aluminium depend on chemical form, dose and route of exposure. Pure aluminium, its ions and its compounds can have very different biological and environmental effects, so safety data should be checked for the actual substance being handled.