Polonium (Po)
Element 84 · Metalloid · atomic mass [209] u · group 16, period 6
Electron shells: 2, 8, 18, 32, 18, 6
Polonium is intensely radioactive — a gram generates enough heat to glow. It is one of the most toxic substances known by mass.
Marie Curie named it after Poland, then under partition, as a deliberate political statement.
- Atomic number
- 84
- Atomic mass
- [209] u
- Electron configuration
- [Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁴
- Group · period · block
- 16 · 6 · p
- Oxidation states
- −2, +2, +4
- Electronegativity
- 2 (Pauling)
- Melting point
- 254 °C
- Boiling point
- 962 °C
- Density
- 9.32 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery-grey metal
- Discovered
- Marie and Pierre Curie, 1898
84 protons, and 84 electrons when neutral
Mass number of the longest-lived isotope — no standard atomic weight exists
Chalcogens
What Polonium is used for
- Anti-static brushes for film and instruments
- Spacecraft heat sources
- Neutron source initiators
Atomic structure of Polonium
A neutral polonium atom has 84 protons and 84 electrons. Its most common isotope carries about 125 neutrons, which is where the mass number 209 comes from. Change the neutron count and you have a different isotope of polonium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 18, 6. In orbital notation that is [Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁴, leaving 6 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Polonium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Polonium sits in the periodic table
Elements on the staircase between metals and non-metals, showing properties of both. Their intermediate conductivity is what makes semiconductors possible.
- Directly above: Tellurium — same group, so similar chemistry with a smaller atom.
- Directly below: Livermorium — same group, one shell larger.
- One proton lighter: Bismuth.
- One proton heavier: Astatine.
Discovery and naming
Polonium was discovered by Marie and Pierre Curie in 1898. Its name comes from Poland, Marie Curie's homeland.
Every isotope of polonium is radioactive, so it has no standard atomic weight. Periodic tables show the mass number of its longest-lived isotope in square brackets instead.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Polonium?
Polonium has no stable isotope, so it has no standard atomic weight. Periodic tables instead show 209 in square brackets — the mass number of its longest-lived isotope.
How many protons, neutrons and electrons does Polonium have?
Polonium has 84 protons, because the atomic number is the proton count and that is what makes an atom Polonium at all. A neutral Polonium atom has the same number of electrons, 84. The neutron count varies by isotope; the most common one has about 125, since 209 − 84 = 125.
What is the electron configuration of Polonium?
The electron configuration of Polonium is [Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁴. Its electrons are arranged 2, 8, 18, 32, 18, 6 across 6 shells.
Is Polonium a metal?
Not quite. Polonium is a metalloid — it sits on the staircase dividing metals from non-metals and shows properties of both, which is exactly why metalloids matter to the semiconductor industry.
What group and period is Polonium in?
Polonium is in group 16 (the chalcogens), period 6, in the p-block. The group is its column and the period is its row.
What is the charge of Polonium?
Polonium most commonly forms a 4+ or 2+ ion. It has 6 outer electrons available to lose. Across all its compounds it shows oxidation states of −2, +2, +4.
What is the melting point of Polonium?
Polonium melts at 254 °C and boils at 962 °C. That puts it in the solids at everyday temperatures.
What is Polonium used for?
Anti-static brushes for film and instruments, Spacecraft heat sources, Neutron source initiators. Polonium is intensely radioactive — a gram generates enough heat to glow.
Who discovered Polonium, and where does its name come from?
Polonium (Po) was discovered by Marie and Pierre Curie in 1898. The name comes from Poland, Marie Curie's homeland.
Is Polonium radioactive?
Yes. Every isotope of Polonium is radioactive — it has no stable form at all, which is why the periodic table shows its mass in square brackets rather than as a standard atomic weight.