Polonium at a glance
- Atomic number
- 84
- Symbol
- Po
- Atomic mass
- 209 u
- Category
- Post-transition metal
- Group / period
- 16 / 6
- Electron configuration
- [Xe] 4f 14 5d 10 6s 2 6p 4
- State at 25 °C
- Solid
- Melting point
- 253.9 °C
- Boiling point
- 961.9 °C
- Density
- 9.32 g/cm³
- Electronegativity
- 2
- 1st ionization energy
- 812 kJ/mol
- Oxidation states
- +4, +2
- Discovered
- 1898
Atomic structure
A neutral polonium atom has 84 protons and 84 electrons, and its most common isotope carries about 125 neutrons. One atom weighs about 3.47 × 10⁻²⁵ kg, so a mole of polonium (6.022 × 10²³ atoms) weighs 209 g. That nucleus holds 1.49 neutrons for every proton, typical of heavy nuclei, which need extra neutrons to hold together against the protons' repulsion. The electrons fill 6 shells (K 2, L 8, M 18, N 32, O 18, P 6), which gives the configuration [Xe] 4f 14 5d 10 6s 2 6p 4. With 6 electrons in its outer shell, it tends to gain or share electrons to complete its outer shell. All of its isotopes are radioactive, so any polonium on Earth is either freshly made or part of a decay chain.
Physical properties
At room temperature (25 °C) polonium is a solid. It melts at 253.9 °C and boils at 961.9 °C, so it stays liquid across a 708-degree range. It stays solid in a hot kitchen oven but would melt in a candle flame (about 1000 °C). Its density is 9.32 g/cm³, 9.32 times as dense as water. Its atoms have a radius of about 190 pm (Bismuth next door is 160 pm). In the solid, its atoms pack into a simple cubic lattice.
Chemical behaviour
Its electronegativity is 2 on the Pauling scale. Pulling off its outermost electron takes 812 kJ/mol, less than Tellurium above it (869 kJ/mol). A bond between polonium and chlorine would be polar covalent, with an electronegativity difference of 1.2. It releases 136 kJ/mol when it gains an extra electron. Its common oxidation states are +4, +2, so in compounds you will usually meet it as Po⁴⁺ and Po²⁺. Group 16 also holds Oxygen, Sulfur, Selenium, Tellurium and Livermorium, which share its outer-shell pattern. Its Lewis symbol is Po surrounded by 6 dots. Handle with care: as a pure element it is radioactive.
Where it comes from
It makes up 2e-10 mg/kg of Earth's crust, the 87th most abundant element there. It was first identified in 1898, making it the 80th element to be discovered (counting the 11 known since antiquity together).