Post-transition metalElement 84 · p-block

Polonium (Po)

Polonium (Po) is a post-transition metal with atomic number 84; its most stable known isotope has mass number 209. At room temperature it is a solid that melts at 254 °C and boils at 962 °C.

84PoPolonium[209]

Atomic number

protons

Atomic weight

[209]

most stable isotope

Melting point

254 °C

527.15 K

Boiling point

962 °C

1,235.15 K

Density

9.2 g/cm³

near room temperature

Electronegativity

Pauling scale

State at 25 °C

Solid

Discovered

1898

France

Polonium at a glance

Identity

Symbol	Po
Atomic number (Z)	84
Atomic weight	[209] mass number of the most stable isotope
Category	Post-transition metal
Group	16 — chalcogens (oxygen group)
Period	6
Block	p-block
CAS number	7440-08-6

Atomic properties

Electron configuration	[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁴ Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁴
Electrons per shell	2, 8, 18, 32, 18, 6
Oxidation states	-2, +2, +4 Less common: +5, +6
Electronegativity (Pauling)	2
First ionisation energy	8.418 eV (812.2 kJ/mol) 2nd: 19.3 eV · 3rd: 27.3 eV
Electron affinity	1.9 eV
Atomic radius (empirical)	190 pm
Covalent radius	145 pm
Van der Waals radius	197 pm

Physical properties

State at 25 °C	Solid
Melting point	254 °C · 489.2 °F · 527.15 K
Boiling point	962 °C · 1,763.6 °F · 1,235.15 K
Density	9.2 g/cm³
Crystal structure	Simple cubic

Isotopes & abundance

Natural occurrence	From radioactive decay
Radioactive	Yes
Most stable isotope	²⁰⁹Po — half-life 124 years
Known isotopes	42
Abundance in Earth's crust	0 mg/kg
Abundance in seawater	0 mg/L

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Polonium electron configuration

Polonium has 84 electrons. Written in short form, its ground-state configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁴ — the electrons of the noble gas xenon, plus 4f¹⁴ 5d¹⁰ 6s² 6p⁴.Written out in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁴.

As a member of group 16 it has 6 valence electrons in its outer shell (shell 6), which largely decide its chemistry.

4f↑↓↑↓↑↓↑↓↑↓↑↓↑↓

5d↑↓↑↓↑↓↑↓↑↓

6s↑↓

6p↑↓↑↑

Discovery and name

Discovered

1898 — Marie and Pierre Curie · France.

Name

Poland, Marie Curie's homeland.

Known for

Intensely radioactive. Polonium-210 has been used in anti-static brushes and as a heat source in early space probes; it is extremely toxic.

Isotopes of polonium

Polonium has no stable isotopes. Its longest-lived known isotope is:

Isotope	Protons	Neutrons	Half-life
²⁰⁹Po	84	125	124 years

42 isotopes of polonium are known in our data set (half-lives as published in nuclear data tables).

Polonium compared with group 16

The other elements in group 16 (chalcogens (oxygen group)), from top to bottom of the table:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Oxygen	8	15.999	-219 °C	-183 °C	1.429 g/L	3.44
Sulfur	16	32.06	115 °C	445 °C	2.07 g/cm³	2.58
Selenium	34	78.971	221 °C	685 °C	4.809 g/cm³	2.55
Tellurium	52	127.60	450 °C	988 °C	6.232 g/cm³	2.1
Polonium	84	[209]	254 °C	962 °C	9.2 g/cm³	2
Livermorium	116	[293]	—	—	12.9 g/cm³ (pred.)	—

Frequently asked questions

6 answers

What is the atomic mass of polonium?

Polonium has no stable isotopes, so it has no standard atomic weight. Periodic tables show [209], the mass number of its most stable known isotope.

How many protons, neutrons and electrons does polonium have?

A neutral polonium atom has 84 protons and 84 electrons. Its most stable isotope, polonium-209, has 125 neutrons.

What is the electron configuration of polonium?

[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁴ (in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁴).

What are the melting and boiling points of polonium?

Polonium melts at 254 °C (489.2 °F) and boils at 962 °C (1,763.6 °F).

Is polonium a metal?

Polonium is a metal. It is in group 16, period 6, and is a solid at room temperature.

Who discovered polonium?

1898 — Marie and Pierre Curie (France).