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] 3s¹
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, 1
Number of electrons in each shell, from the nucleus outwards.
97.8 °C (370.95 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.
883 °C (1,156 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).
0.97 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
0.93 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.
5.139 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.
0.548 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.
166 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.
+1
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Sodium (Na) is a chemical element with atomic number 11. It sits in group 1 and period 3 of the periodic table, in the s-block. It is an alkali metal. At room temperature it is a solid. Its standard atomic weight is 22.990.
Origin of the name
Humphry Davy, who isolated the metal in 1807 by passing electricity through molten caustic soda, named it sodium after soda. The symbol Na comes from the Latin name natrium, after natron, a natural soda collected in Egypt since antiquity. In the Middle Ages a sodium compound called sodanum was taken for headaches.
Where is sodium found?
Sodium is too reactive ever to occur free, yet it is the sixth most abundant element in the Earth’s crust, about 2.5%. Most of it is in salt: rock salt (halite) and the oceans, where every litre of sea water holds about 10.5 g of sodium.
What is sodium used for?
Sodium is used mostly in its compounds. Table salt flavours and preserves food and keeps winter roads free of ice; soda ash goes into glass, caustic soda into soap and paper, and baking soda makes dough rise. The metal itself fills the yellow-orange sodium-vapour street lamps and, as a liquid, cools some fast nuclear reactors.
Interesting facts
Sodium is so soft that it can be cut with a knife.
Sodium reacts violently with water, so the metal is kept away from moisture, usually under oil.
Every nerve impulse in your body begins with sodium ions rushing into a nerve cell.