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 4d⁵
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, 13, 2
Number of electrons in each shell, from the nucleus outwards.
2,157 °C (2,430 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.
4,265 °C (4,538 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).
11 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
1.9 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.
7.119 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 data
Energy released when a neutral atom gains an electron. Highest for the halogens. Noble gases, nitrogen and some metals form no stable negative ion.
147 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.
+7, +6, +4
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Technetium (Tc) is a chemical element with atomic number 43. It sits in group 7 and period 5 of the periodic table, in the d-block. It is a transition metal. At room temperature it is a solid. It has no standard atomic weight; the mass number of its most stable isotope is 97.
Origin of the name
Technetium was the first element made by people rather than found in nature, hence its name, from the Greek technētos, ‘artificial’. Dmitri Mendeleev had left a gap for it below manganese, and in 1925 its discovery was announced under the name masurium, wrongly. In 1937 Carlo Perrier and Emilio Segrè in Italy found it in a piece of molybdenum that had been bombarded in a cyclotron in Berkeley.
Where is technetium found?
On Earth technetium exists only as the faintest traces, formed when uranium in its ores splits. Yet it has been found in the light of certain stars, and since technetium does not last for billions of years, this proved that stars make heavy elements themselves. Today it is produced in nuclear reactors.
What is technetium used for?
Technetium-99m is one of the most important substances in nuclear medicine. Injected into the body, it gives off gamma rays that a camera turns into images of bones, the heart, the kidneys and other organs, and it vanishes within a day or so. Technetium also protects steel from corrosion, but because it is radioactive this is used only in closed systems.
Interesting facts
All forms of technetium are radioactive. Of the elements lighter than bismuth, only technetium and promethium have no stable isotopes.