Francium (Fr)
Element 87 · Alkali metal · atomic mass [223] u · group 1, period 7
Electron shells: 2, 8, 18, 32, 18, 8, 1
Francium is the most unstable of the first 101 elements, with a half-life of just 22 minutes. Only a few thousand atoms have ever existed in one place at once.
At any given moment the entire Earth's crust contains less than 30 grams of francium.
- Atomic number
- 87
- Atomic mass
- [223] u
- Electron configuration
- [Rn] 7s¹
- Group · period · block
- 1 · 7 · s
- Oxidation states
- +1
- Electronegativity
- 0.7 (Pauling)
- Melting point
- 26.85 °C
- Boiling point
- —
- Density
- Not measured
- State at 20 °C
- Solid
- Appearance
- Unknown; presumed metallic
- Discovered
- Marguerite Perey, 1939
87 protons, and 87 electrons when neutral
Mass number of the longest-lived isotope — no standard atomic weight exists
Alkali metals
What Francium is used for
- Atomic structure research only
Atomic structure of Francium
A neutral francium atom has 87 protons and 87 electrons. Its most common isotope carries about 136 neutrons, which is where the mass number 223 comes from. Change the neutron count and you have a different isotope of francium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 18, 8, 1. In orbital notation that is [Rn] 7s¹, leaving 1 valence electron in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Francium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Francium sits in the periodic table
Discovery and naming
Francium was discovered by Marguerite Perey in 1939. Its name comes from France.
Every isotope of francium 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 Francium?
Francium has no stable isotope, so it has no standard atomic weight. Periodic tables instead show 223 in square brackets — the mass number of its longest-lived isotope.
How many protons, neutrons and electrons does Francium have?
Francium has 87 protons, because the atomic number is the proton count and that is what makes an atom Francium at all. A neutral Francium atom has the same number of electrons, 87. The neutron count varies by isotope; the most common one has about 136, since 223 − 87 = 136.
What is the electron configuration of Francium?
The electron configuration of Francium is [Rn] 7s¹. Its electrons are arranged 2, 8, 18, 32, 18, 8, 1 across 7 shells.
Is Francium a metal?
Yes. Francium is classified as a alkali metal, on the left side of the table.
What group and period is Francium in?
Francium is in group 1 (the alkali metals), period 7, in the s-block. The group is its column and the period is its row.
What is the charge of Francium?
Francium most commonly forms a 1+ ion. It has 1 electron in its outer shell and loses it readily, which is what the group number tells you.
What is the melting point of Francium?
Francium melts at 26.85 °C. That puts it in the solids at everyday temperatures.
What is Francium used for?
Atomic structure research only. Francium is the most unstable of the first 101 elements, with a half-life of just 22 minutes.
Who discovered Francium, and where does its name come from?
Francium (Fr) was discovered by Marguerite Perey in 1939. The name comes from France.
Is Francium radioactive?
Yes. Every isotope of Francium 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.