Francium

Symbol: Fr
Atomic number: 87
Category: alkali metals
Group: 1
Period: 7
Block: s
Atomic weight: [223] g/mol
Electrons per shell: 2, 8, 18, 32, 18, 8, 1
CAS number: 7440-73-5
Phase: solid
Density: 1.87 kg/dm³ (near room temperature)
Melting point: 300 K (27 °C, 80 °F)
Boiling point: 950 K (677 °C, 1250 °F)
Crystal structure: cubic body centered
Oxidation states: 1
Electronegativity: 0.7 (Pauling scale)
Name's origin: francium
Name's meaning: France, the discoverer's homeland
Facts:
- all isotopes of francium decay into either astatine, radium, or radon
- was formerly known as eka-caesium and actinium K
- as little as 20-30 g of francium-223 exists at any given time throughout the Earth's crust
- is the least stable of the naturally occurring elements: its most stable isotope, francium-233 has a half-life of only 22 minutes
- has the lowest electronegativity of all the known elements at 0.7 on the Pauling scale