Beryllium (Be)

Beryllium is stiffer than steel at a quarter of the weight, which is why the James Webb Space Telescope's 18 mirror segments are made of it — it barely changes shape as it cools to 40 K. It is also one of the more insidious industrial poisons: inhaled dust causes chronic beryllium disease in a minority of exposed people, a permanent lung condition driven by an immune response, and the susceptible fraction is largely genetic. Beryllium-8, the isotope two helium nuclei would form, falls apart in about 10⁻¹⁶ seconds, and the fact that stars have to build carbon through a fleeting three-body collision instead is one of the sharper coincidences in physics.

Properties

Atomic number

4

Symbol

Be

Standard atomic weight

9.0122 u

Category

Alkaline earth metal

Group

2

Period

2

Block

s-block

Electron configuration

[He] 2s²

Electrons per shell

2, 2

Melting point

1,560 K — 1286.8 °C — 2348.3 °F

Boiling point

2,744 K — 2470.8 °C — 4479.5 °F

Density

1.85 g/cm³

Electronegativity

1.57 (Pauling)

Oxidation states

+2

Discovered

1798 by Louis-Nicolas Vauquelin

Electron configuration

Full

1s² 2s²

Noble gas shorthand

[He] 2s²

Shells

K: 2 · L: 2

What it is used for

• X-ray tube windows, because it is nearly transparent to X-rays
• Beryllium-copper tools that will not spark in a gas atmosphere
• Mirrors for the James Webb Space Telescope
• Neutron reflectors and moderators in research reactors
• Stiff, light structures in satellites and inertial guidance systems

Hazards

• Inhaled dust or fume causes chronic beryllium disease, which is incurable
• Classified as a human carcinogen
• Machining, grinding and welding are the dangerous operations, not handling solid metal

Neighbours in the table

Group 2

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Beryllium sits in group 2 with magnesium, calcium, strontium, barium, radium.