Francium (Fr): electron configuration, atomic mass and facts
Francium (Fr) is element 87 of the periodic table, an alkali metal in period 7, group 1. Its electron configuration is [Rn] 7s1, with electrons arranged in shells 2, 8, 18, 32, 18, 8, 1, and its most stable isotope has mass number 223.
▶ Watch Francium’s electrons orbit in the interactive periodic tableFrancium at a glance
| Symbol | Fr |
|---|---|
| Atomic number | 87 |
| Atomic mass | [223] u (most stable isotope) |
| Category | Alkali metal |
| Group | 1 |
| Period | 7 |
| Block | s-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 7s1 |
| Noble-gas shorthand | [Rn] 7s1 |
| Electrons per shell | 2, 8, 18, 32, 18, 8, 1 |
| Outer-shell electrons | 1 |
| Electronegativity (Pauling) | 0.7 |
| State at 20 °C | solid |
Where is Francium on the periodic table?
Francium is in period 7, group 1, in the s-block. The period number matches its 7 electron shells, and the block names the subshell its last electrons fill. In the same group, Caesium sits directly above it. Elements in one group have the same number of outer-shell electrons (1 here), which is why they react in similar ways.
How to work out the electron configuration of Francium
Put 87 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20), 3d¹⁰ (30), 4p⁶ (36), 5s² (38), 4d¹⁰ (48), 5p⁶ (54), 6s² (56), 4f¹⁴ (70), 5d¹⁰ (80), 6p⁶ (86), 7s¹ (87). In shorthand, [Rn] stands for the 86 electrons of radon, giving [Rn] 7s¹.
How electronegative is Francium?
Francium has a Pauling electronegativity of 0.7, ranking 100 of the 100 elements with a known value (fluorine is highest at 3.98). That is low: it tends to give up electrons and form positive ions.
Frequently asked questions
What is the electron configuration of Francium?
The electron configuration of Francium (Fr) is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 7s1. In noble-gas shorthand it is written [Rn] 7s1.
How many electrons does Francium have in each shell?
Francium has 87 electrons arranged in shells as 2, 8, 18, 32, 18, 8, 1. It has 1 electron in its outer shell.
What is the atomic mass of Francium?
Francium has no stable isotopes. Its most stable isotope has a mass number of 223.
Is Francium a metal?
Yes. Francium is an alkali metal.
Explore nearby elements
More alkali metals: Lithium, Sodium, Potassium, Rubidium, Caesium. See all elements on the periodic table.