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.
[Ne] 3s² 3p³
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, 8, 5
Number of electrons in each shell, from the nucleus outwards.
44.2 °C (317.3 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.
280.5 °C (553.65 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).
1.82 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
2.19 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.
10.487 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.
0.747 eV
Energy released when a neutral atom gains an electron. Highest for the halogens. Noble gases, nitrogen and some metals form no stable negative ion.
107 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.
+5, +3, -3
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Phosphorus (P) is a chemical element with atomic number 15. It sits in group 15 and period 3 of the periodic table, in the p-block. It is a nonmetal. At room temperature it is a solid. Its standard atomic weight is 30.974.
Origin of the name
The name is Greek phōsphóros, ‘light-bearer’, because white phosphorus glows in the dark. The Greeks also called the morning star, the planet Venus, by this name. The word phosphorescence comes from it too.
Where is phosphorus found?
Phosphorus is too reactive to occur free; it is found in phosphate minerals, and phosphate rock rich in apatite is its main source. Every living thing needs it: phosphorus is part of DNA, RNA and ATP, the molecule cells use to carry energy, and our bones and teeth are made mostly of calcium phosphate.
What is phosphorus used for?
Most phosphorus is turned into fertilisers, since crops need it to grow. Red phosphorus is on the striking strip of matchboxes. Phosphates are also used as food additives and in cleaning agents.
Interesting facts
In 1669 the alchemist Hennig Brand, searching for the philosopher’s stone, boiled down dozens of buckets of urine and obtained a white substance that glowed in the dark: phosphorus.
Phosphorus was the first element discovered by a person known by name; the elements known before it had been used since antiquity.
White phosphorus catches fire by itself in air, so it is kept under water; red phosphorus is far safer.