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.
[Kr] 5s¹ 4d⁸
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, 18, 16, 1
Number of electrons in each shell, from the nucleus outwards.
1,964 °C (2,237 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.
3,695 °C (3,968 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).
12.4 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
2.28 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.
7.459 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.
1.143 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.
142 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.
+3
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Rhodium (Rh) is a chemical element with atomic number 45. It sits in group 9 and period 5 of the periodic table, in the d-block. It is a transition metal. At room temperature it is a solid. Its standard atomic weight is 102.91.
Origin of the name
The name comes from the Greek rhodon, ‘rose’, because solutions of its salts are rose-coloured. William Hyde Wollaston discovered rhodium in 1803 in platinum ore from South America, soon after he had found palladium in the same kind of ore.
Where is rhodium found?
Rhodium is one of the rarest and most valuable of all metals. It occurs with platinum and is obtained as a by-product of refining platinum and of nickel mining.
What is rhodium used for?
Most rhodium goes into the catalytic converters of cars, where it helps turn harmful exhaust gases into harmless ones. Alloyed with platinum, it makes crucibles, temperature sensors and spark-plug electrodes that withstand great heat. A thin coat of rhodium gives white-gold and silver jewellery its bright shine and keeps it from tarnishing, and rhodium-coated mirrors are hard and highly reflective.