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 4d²
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, 10, 2
Number of electrons in each shell, from the nucleus outwards.
1,855 °C (2,128 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.
4,409 °C (4,682 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).
6.52 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
1.33 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.
6.634 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.
0.433 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.
175 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.
+4
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Zirconium (Zr) is a chemical element with atomic number 40. It sits in group 4 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 91.222.
Origin of the name
The element is named after the mineral zircon, a gemstone known since antiquity, whose name goes back to zargun, ‘gold-like’. In 1789 Martin Heinrich Klaproth analysed a zircon and found the oxide of a new element in it. Jöns Jacob Berzelius obtained the impure metal in 1824, but pure zirconium was made only in 1914.
Where is zirconium found?
Zirconium is obtained mainly from the mineral zircon, a zirconium silicate. Its ores always contain hafnium as well, an element so similar that the two are very hard to separate.
What is zirconium used for?
Zirconium hardly absorbs neutrons and does not corrode, so about 90% of the metal is made into the tubes that hold uranium fuel in nuclear reactors. Zirconium dioxide withstands enormous heat and lines furnaces and crucibles, and the metal is used for pumps and pipes in chemical plants. Zircon and synthetic cubic zirconia are cut into gems that look like diamonds.
Interesting facts
Zirconium for reactors has to be almost completely free of hafnium, because hafnium, unlike zirconium, absorbs neutrons strongly.