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.
[Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁴
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, 32, 18, 6
Number of electrons in each shell, from the nucleus outwards.
254 °C (527 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.
962 °C (1,235 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).
9.32 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
2.0 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.
8.418 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.
140 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, +2, -2
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Polonium (Po) is a chemical element with atomic number 84. It sits in group 16 and period 6 of the periodic table, in the p-block. It is a metalloid. At room temperature it is a solid. It has no standard atomic weight; the mass number of its most stable isotope is 209.
Origin of the name
Polonium is named after Poland, the homeland of Marie Curie. At the time Poland did not exist as a state: its land was divided between neighbouring empires, and the name was meant to draw attention to that. In 1898 Marie and Pierre Curie noticed that the uranium ore pitchblende was more radioactive than the uranium extracted from it, and tracked down the cause: a new element, polonium, and soon after radium. They had to process tons of ore to obtain tiny amounts.
Where is polonium found?
Polonium occurs in uranium ores in vanishingly small amounts, about a tenth of a milligram per ton. The polonium used today is made in nuclear reactors from bismuth.
What is polonium used for?
Polonium is used in devices that remove static electricity in factories and, combined with beryllium, as a source of neutrons. Because it gives off a great deal of heat, it once warmed the Soviet Lunokhod rovers on the Moon.
Interesting facts
Polonium is one of the most poisonous substances known. In 2006 the former Russian intelligence officer Alexander Litvinenko died in London after being poisoned with polonium-210.
Tobacco smoke contains tiny amounts of radioactive polonium.