Francium (Fr)
Element 87 · alkali metal · group 1, period 7
Francium is element 87, a alkali metal in group 1 and period 7. Its electron configuration is [Rn] 7s1. That leaves 1 valence electron in the outer shell, with the shells filling 2, 8, 18, 32, 18, 8, 1. Losing its 1 valence electron is the shorter route to a full shell, so it carries a charge of +1.
- 87 protons
- 1 valence e−
- +1
- s-block
Properties
| Atomic number | 87 |
|---|---|
| Symbol | Fr |
| Standard atomic weight | 223 u |
| Group | 1 |
| Period | 7 |
| Block | s-block |
| Category | alkali metal |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 7s1 |
| Noble-gas notation | [Rn] 7s1 |
| Electrons per shell | 2, 8, 18, 32, 18, 8, 1 |
| Valence electrons | 1 |
| Common ionic charge | +1 |
| Electronegativity (Pauling) | 0.7 |
| Protons / electrons | 87 / 87 |
Electron configuration of francium
Orbitals fill from the lowest energy upward. Writing that out for francium gives 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 7s1, which is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 7s1 in plain text.
Everything up to Rn is the same as in that noble gas, so it is usually abbreviated to [Rn] 7s1. The part outside the bracket is what does the chemistry.
| Subshell | Electrons | Capacity |
|---|---|---|
| 1s | 2 | 2 |
| 2s | 2 | 2 |
| 2p | 6 | 6 |
| 3s | 2 | 2 |
| 3p | 6 | 6 |
| 3d | 10 | 10 |
| 4s | 2 | 2 |
| 4p | 6 | 6 |
| 4d | 10 | 10 |
| 4f | 14 | 14 |
| 5s | 2 | 2 |
| 5p | 6 | 6 |
| 5d | 10 | 10 |
| 6s | 2 | 2 |
| 6p | 6 | 6 |
| 7s | 1 | 2 |
Francium ion charge
Francium commonly forms ions with a charge of +1.
It has 1 valence electron, so it is 7 short of a full octet and 1 above an empty outer shell. An atom takes whichever route is shorter, which is why the charge comes out as it does.
Common questions
How many valence electrons does francium have?
Francium has 1 valence electron. For groups 1 and 2 the count is the group number, and francium is in group 1.
What is the electron configuration of francium?
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 7s1, or [Rn] 7s1 written from the previous noble gas. Orbitals fill lowest energy first.
What is the charge of francium?
Francium commonly forms ions with a charge of +1. With 1 valence electron it is 7 short of an octet and 1 above an empty shell, so it takes whichever route is shorter.
How many protons, electrons and neutrons does francium have?
A neutral francium atom has 87 protons and 87 electrons. Its standard atomic weight is 223, so the most common isotope has about 136 neutrons.
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