Periodic table of the chemical elements
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86 Rn,Radon
Noble gases · Gas
Atomic mass [222] mass number of the most stable isotope
86
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.
How electrons are arranged in subshells. The bracket stands for the previous noble gas; the superscript is the number of electrons in a subshell.
Number of electrons in each shell, from the nucleus outwards.
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.
Temperature at which the liquid boils at standard pressure. For carbon and arsenic, the temperature at which the solid turns straight into vapour (sublimation).
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
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.
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.
Energy released when a neutral atom gains an electron. Highest for the halogens. Noble gases, nitrogen and some metals form no stable negative ion.
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.
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Radon (Rn) is a chemical element with atomic number 86. It sits in group 18 and period 6 of the periodic table, in the p-block. It is a noble gas. At room temperature it is a gas. It has no standard atomic weight; the mass number of its most stable isotope is 222.
Radon is named after radium, which gives it off. In 1899 Ernest Rutherford and Robert Owens noticed that thorium released a radioactive gas, and in 1900 Friedrich Ernst Dorn found the gas given off by radium. It was first called ‘radium emanation’ and then niton, from the Latin for ‘shining’; the name radon has been used since 1923.
Radon forms all the time from the decay of uranium and radium in rocks and soil. It seeps out of the ground and can build up in houses, especially in basements; how much there is varies greatly from place to place.
Radon was once sealed in tiny tubes and placed in tumours to treat cancer, but this has largely been given up. Today it is mostly a substance to measure and keep out of homes.