Average mass of an atom in unified atomic mass units (1 u is 1/12 of the mass of a carbon-12 atom). Accounts for the natural mix of the element’s isotopes.
Number of the vertical column, 1 to 18 in IUPAC numbering. Elements in a group share the same outer-shell layout, so their properties are alike.
Number of the horizontal row. Usually equal to the number of electron shells in the atom; palladium is the exception, with four shells in period 5.
The subshell (s, p, d or f) that receives the last electrons in the usual filling order; it divides the table into four blocks. Real atoms sometimes differ: lanthanum starts the f-block but has no f electrons.
[He] 2s²
How electrons are arranged in subshells. The bracket stands for the previous noble gas; the superscript is the number of electrons in a subshell.
2, 2
Number of electrons in each shell, from the nucleus outwards.
1,287 °C (1,560 K)
Temperature at which the solid turns liquid at standard pressure. Helium, carbon and arsenic do not melt at normal pressure: helium needs about 25 atm, carbon and arsenic turn straight into vapour.
2,471 °C (2,744 K)
Temperature at which the liquid boils at standard pressure. For carbon and arsenic, the temperature at which the solid turns straight into vapour (sublimation).
1.85 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
1.57 Pauling
How strongly an atom pulls electrons towards itself in a chemical bond. On the Pauling scale it runs from 0.79 for caesium to 3.98 for fluorine.
9.323 eV
Energy needed to remove the most loosely bound electron from an atom. The lower it is, the more easily the element gives up an electron, which is typical of metals.
no stable negative ion
Energy released when a neutral atom gains an electron. Highest for the halogens. Noble gases, nitrogen and some metals form no stable negative ion.
96 pm
Half the length of a single covalent bond between two atoms of the element. It shows the size of an atom inside a molecule or crystal: 76 pm for carbon, 132 pm for iron.
+2
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Beryllium (Be) is a chemical element with atomic number 4. It sits in group 2 and period 2 of the periodic table, in the s-block. It is an alkaline earth metal. At room temperature it is a solid. Its standard atomic weight is 9.0122.
Origin of the name
Beryllium is named after the mineral beryl, Greek bḗryllos, in which Louis-Nicolas Vauquelin found it in 1798. Because its salts taste sweet, it was first called glucinium, from Greek glykýs ‘sweet’; the name beryllium was used by Friedrich Wöhler, who isolated the metal in 1828.
Where is beryllium found?
Beryllium is rare: about 2–6 parts per million of the Earth’s crust. Stars do not make it; it forms in space when cosmic rays split heavier nuclei. Its main ores are beryl and bertrandite. Emerald and aquamarine are gem varieties of beryl: emerald owes its green to a trace of chromium.
What is beryllium used for?
Beryllium lets X-rays through almost unhindered, so it makes the windows of X-ray tubes. A little of it in copper gives beryllium copper, a hard alloy for springs, electrical contacts and tools that strike no sparks. Light and very stiff, the metal is used in aircraft, satellites and spacecraft, and in nuclear reactors it reflects and slows neutrons.
Interesting facts
Early chemists tasted beryllium salts to check their sweetness, but beryllium is toxic: its dust can cause berylliosis, a chronic lung disease.
Hit by alpha particles, beryllium gives off neutrons, which is why it is used in laboratory neutron sources.