Polonium (Po)

Polonium-210 puts out about 140 watts of heat per gram from alpha decay alone — a half-gram pellet glows red hot in the dark and will melt itself. Marie Curie found it first, before radium, and named it after Poland, which did not then exist as a country; she was making a political point in a chemistry paper. It became infamous in 2006 when Alexander Litvinenko was killed with a dose in a cup of tea: alpha radiation does not penetrate skin or a teapot, so it is harmless outside the body and catastrophic inside it, which is exactly what makes it a poison rather than a hazard.

Properties

Atomic number

84

Symbol

Po

Mass number of most stable isotope

[209]

Category

Metalloid

Group

16

Period

6

Block

p-block

Electron configuration

[Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁴

Electrons per shell

2, 8, 18, 32, 18, 6

Melting point

527 K — 253.9 °C — 488.9 °F

Boiling point

1,235 K — 961.9 °C — 1763.3 °F

Density

9.32 g/cm³

Electronegativity

2 (Pauling)

Oxidation states

+4, +2

Discovered

1898 by Marie and Pierre Curie

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁴

Noble gas shorthand

[Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁴

Shells

K: 2 · L: 8 · M: 18 · N: 32 · O: 18 · P: 6

What it is used for

• Antistatic brushes for cleaning camera lenses and film
• Heat sources for early space probes, including Lunokhod
• Neutron initiators in early nuclear weapon designs

Hazards

• Around 250 billion times more toxic by mass than hydrogen cyanide when ingested
• Emits alpha particles that are stopped by paper but devastating internally
• Volatile enough to spread as contamination at room temperature

No stable isotope; the mass given is the mass number of polonium-209, the longest-lived at about 124 years. Filed as a metalloid following the CRC and PubChem classification, though its bulk properties are those of a metal and several periodic tables call it a post-transition metal.

Neighbours in the table

Group 16

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Polonium sits in group 16 with oxygen, sulfur, selenium, tellurium, livermorium.