87 Fr

Francium (Fr)

Element 87 · Alkali metal · Solid at 25 °C · Group 1, Period 7

Francium is vanishingly rare and intensely unstable — its longest-lived isotope lasts only about 22 minutes.

On the periodic table, francium sits in group 1 — the alkali metal group — in period 7. It is one of 6 elements classified as an alkali metal, and at room temperature (25 °C) it is a solid.

The alkali metals are soft, silvery metals with a single electron in their outer shell — which they give up so easily that they are among the most reactive metals known. They react vigorously (sometimes violently) with water, tarnish in air within minutes, and are never found as free metals in nature. In the lab they are stored under oil to keep air and moisture away. Reactivity increases as you move down the group.

Properties of francium

Properties of Francium
Atomic number (Z)	87
Symbol	Fr
Atomic mass	(223) (mass number of the most stable isotope; this element has no standard atomic weight)
Category	Alkali metal
Group	1
Period	7
Block	s-block
Metal / nonmetal	Metal
State at 25 °C	Solid
Electron configuration	[Rn] 7s1
Electronegativity (Pauling)	0.7
Melting point	27 °C (300.15 K / 80.6 °F)
Boiling point	677 °C (950.15 K / 1,250.6 °F)
Density	—

Position in the periodic table

Francium shares group 1 — the alkali metal group with Hydrogen (H), Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs). Elements in the same group have the same number of outer electrons, so they tend to behave alike chemically — comparing them is one of the fastest ways to see periodic trends in action.

Physical properties

Francium melts at 27 °C (300.15 K / 80.6 °F) and boils at 677 °C (950.15 K / 1,250.6 °F), giving it a liquid range of about 650 °C at standard pressure.

Data notes

The atomic mass is shown in parentheses because this element has no standard atomic weight; the number given is the mass number of its most stable known isotope.