Chemical element · reference page

4Be

Beryllium

Beryllium is element 4 (Be), located in period 2, group 2 and the s block. At room temperature its reference phase is solid. Its electron configuration is [He] 2s2.

Atomic number4

Standard atomic weight9.0121831(5)

Group2

Period2

Blocks

Electron configuration[He] 2s2

Electronic structure

What controls its chemistry

The outer configuration ends in s². Removing two valence electrons produces a +2 ion, which is the characteristic ionic state of the alkaline-earth metals.

Compared with group 1 metals, the two-electron outer shell changes ionisation energies, bonding and reactivity. Their compounds commonly occur as oxides, carbonates, sulfates or halides rather than as free metals in nature.

Chemical forms

Compounds, ions and materials

The +2 oxidation state dominates. Oxides, hydroxides, halides, carbonates and sulfates are common families of beryllium compounds, although their solubility and thermal stability vary systematically down group 2.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 1.85 g/cm³. The melting point is 1 556 K (1 283 °C). The boiling point is 2 742 K (2 469 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where beryllium is found and used

In practice, beryllium is encountered in aerospace, x-ray windows and alloys.

In practice

Examples of real uses

Aerospace

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

X-ray windows

Beryllium transmits X-rays unusually well for a structural metal, so thin beryllium windows are used in specialised X-ray equipment.

Alloys

Beryllium is added to metals to change strength, corrosion resistance, melting behaviour or high-temperature performance.

Periodic position

What its neighbours tell us

Beryllium is in period 2 and group 2. In the neighbourhood shown here, lithium is immediately to its left in the same period; magnesium is directly 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

Classificationalkaline earth metal

Phase at room temperatureSolid

Electron shells2 · 2

Density1.85 g/cm³

Melting point1 556 K (1 283 °C)

Boiling point2 742 K (2 469 °C)

Pauling electronegativity1.57

First ionisation energy899.5 kJ/mol

Electron affinity—

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

History

Discovery and identification

The discovery of beryllium is associated with Louis Nicolas Vauquelin. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is 9.0121831(5). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Beryllium 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

Beryllium dust and fumes can cause serious lung disease; industrial exposure must be tightly controlled.