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] 5s² 4d¹⁰
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, 18, 2
Number of electrons in each shell, from the nucleus outwards.
321.1 °C (594.22 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.
767 °C (1,040 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).
8.69 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
1.69 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.
8.994 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.
144 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.
Discovered
1817
Discovered by
Friedrich Stromeyer and Karl Samuel Leberecht Hermann
Cadmium (Cd) is a chemical element with atomic number 48. It sits in group 12 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 112.41.
Origin of the name
The name comes from the Latin cadmia, Greek kadmeia, the ancient name of calamine, a zinc ore; it is linked to Cadmus, the legendary founder of Thebes. In 1817 Friedrich Stromeyer investigated zinc carbonate sold in German pharmacies that turned an unexpected colour when heated, and found the cause: a new metal hidden in the zinc.
Where is cadmium found?
Cadmium has almost no ores of its own. It accompanies zinc, and nearly all of it is obtained as a by-product of refining zinc.
What is cadmium used for?
Cadmium went into rechargeable nickel-cadmium batteries and into plating that protects steel from corrosion. It absorbs neutrons readily, so it is used in the control rods of nuclear reactors, and cadmium sulfide is a brilliant yellow pigment. Because cadmium is poisonous, many of these uses are now restricted.
Interesting facts
Cadmium and its compounds are toxic: long exposure damages the kidneys and lungs.
In 1927 the metre was defined by the wavelength of a red line in the spectrum of cadmium; in 1960 krypton took its place.