Polonium

Polonium (Po) is a post-transition metal with atomic number 84. It has no stable isotope and no characteristic isotopic composition on Earth, so it has no standard atomic weight; its longest-lived isotope has mass number 209. Its electron configuration is [Xe] 4f14 5d10 6s2 6p4, which gives it 6 valence electrons.

Polonium key data

Symbol	Po
Atomic number	84
Mass number (longest-lived isotope)	209
Protons	84
Neutrons (longest-lived isotope, polonium-209)	125
Electrons (neutral atom)	84
Valence electrons	6
Category	Post-transition metal
Period	6
Group	16
Block	p-block
Noble gas notation	[Xe] 4f14 5d10 6s2 6p4
Full electron configuration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p4
Electrons per shell	2, 8, 18, 32, 18, 6

Mass number: IUPAC CIAAW radioactive elements, from NUBASE2020.

Properties of polonium

From PubChem, the US National Institutes of Health. Public domain.

Melting point	527 K (253.85 °C), 77th of 103 by melting point
Boiling point	1235 K (961.85 °C), 69th of 93 by boiling point
Density	9.32 g/cm³, joint 29th of 96 by density
State at room temperature	Solid
Electronegativity	2 (Pauling), joint 31st of 95 by electronegativity
Van der Waals radius	197 pm, joint 63rd of 99 by atomic radius
First ionisation energy	8.417 eV (812.1 kJ/mol), 30th of 102 by first ionisation energy
Predicted electron affinity	1.9 eV (183 kJ/mol), 11th of 57 by electron affinity
Common oxidation states	+4, +2
Discovered	1898

Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.

Polonium electron configuration

The full electron configuration of polonium is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p4. With the noble-gas core collapsed it is [Xe] 4f14 5d10 6s2 6p4, and the outermost subshell is 6p4.

Bohr model of polonium (Po): a nucleus and six shells holding 2, 8, 18, 32, 18 and 6 electrons from the inside out. — Bohr model of polonium (Po). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Orbital box diagram of polonium (Po), [Xe] 4f14 5d10 6s2 6p4, with the xenon core drawn as one bar: one box per orbital, filled by Hund’s rule, showing two unpaired electrons, in 6p. — Orbital diagram of polonium (Po). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one polonium atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

one atom = 209 / (6.02214076 × 10²³)
= 3.4705 × 10⁻²² g

Atoms in one gram

atoms per gram = 6.02214076 × 10²³ / 209
= 2.8814 × 10²¹ atoms

Polonium has no standard atomic weight, because it has neither a stable isotope nor a characteristic isotopic composition on Earth. The figure used above is the mass number of polonium-209, so treat these as nominal.

Polonium on the periodic table

Polonium is in period 6, group 16, in the p-block.

The other elements of group 16 are oxygen, sulfur, selenium, tellurium and livermorium.