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.
[Ar] 4s² 3d¹
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, 9, 2
Number of electrons in each shell, from the nucleus outwards.
1,541 °C (1,814 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.
2,836 °C (3,109 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).
2.99 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
1.36 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.
6.561 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.
0.179 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.
170 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.
Scandium (Sc) is a chemical element with atomic number 21. It sits in group 3 and period 4 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 44.956.
Origin of the name
Lars Fredrik Nilson named scandium after Scandinavia (Latin Scandia): he found it in euxenite and gadolinite, minerals then known only from there. From 10 kg of ore he got about 2 g of pure scandium oxide. His countryman Per Teodor Cleve noticed that the new element was the ‘eka-boron’ Dmitri Mendeleev had predicted a decade earlier, with an atomic weight between those of calcium and titanium: one of the first predictions of the periodic table to come true.
Where is scandium found?
Scandium is not actually rare in the Earth’s crust, but it is spread thinly through many minerals and almost never concentrated. The richest mineral, thortveitite, comes from Scandinavia and Madagascar; nearly all scandium is a by-product of mining uranium, iron and rare earths. In the Sun it ranks far higher among the elements than on Earth.
What is scandium used for?
Metallic scandium was first made only in 1937. A fraction of a percent of it makes aluminium much stronger, and aluminium-scandium alloys went into Soviet MiG fighters, bicycle frames and baseball bats. Scandium iodide in metal-halide lamps gives a light close to sunlight, used to floodlight stadiums for television.
Interesting facts
Although it stands between calcium and titanium, scandium behaves chemically more like yttrium and the rare-earth metals, and it is usually counted as a rare-earth element.