Francium (Fr): Bohr Model, Protons, Neutrons & Electrons
Francium is element number 87, an alkali metal in group 1, period 7. Its atom has 87 protons, 136 neutrons and 87 electrons arranged in 7 shells: 2, 8, 18, 32, 18, 8, 1.
- 87 protons
- 136 neutrons
- 87 electrons
Protons, neutrons and electrons in francium
Le atomic number of francium is 87, so every francium atom has 87 protons. A neutral atom has the same number of electrons, 87. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For francium-223, that is 223 − 87 = 136 neutrons. Every isotope of francium is radioactive; 223 is the mass number of its most stable one.
How to draw the Bohr model of francium
- Draw the nucleus and write 87 p⁺ et 136 n⁰ inside it.
- Draw the first shell and put 2 electrons on it (the first shell holds at most 2).
- Draw the second shell and put 8 electrons on it.
- Draw the third shell and put 18 electrons on it.
- Draw the fourth shell and put 32 electrons on it.
- Draw the fifth shell and put 18 electrons on it.
- Draw the sixth shell and put 8 electrons on it.
- Draw the seventh shell and put 1 electron on it.
- Check: 2 + 8 + 18 + 32 + 18 + 8 + 1 = 87 electrons, the same as the number of protons.
From potassium onwards the shells don’t simply fill as 2, 8, 8: the fourth shell starts before the third is full, so the real arrangement above (2, 8, 18, 32, 18, 8, 1) is the one to draw.
Electron configuration
The electron configuration of francium is [Rn] 7s¹. Its 1 outer electron decides how it reacts: it tends to lose it, forming Fr⁺ ions.
Key facts about francium
| Symbol | Fr |
|---|---|
| Atomic number | 87 |
| Relative atomic mass | [223] |
| Group · period · block | group 1 · period 7 · s-block |
| Type | Métal alcalin |
| State at 25 °C | solid |
| Couches électroniques | 2, 8, 18, 32, 18, 8, 1 |
| Electron configuration | [Rn] 7s¹ |
| Électrons de valence | 1 |
| Common ion | Fr⁺ |
| Electronegativity (Pauling) | 0.70 |
| First ionisation energy | 4.07 eV (393 kJ/mol) |
| Atomic radius (empirical) | — |
Où francium sits on the periodic table
Foire aux questions
How many protons, neutrons and electrons does francium have?
Francium has 87 protons and 87 electrons (atomic number 87). Its most common isotope, francium-223, has 223 − 87 = 136 neutrons.
What is the electron configuration of francium?
[Rn] 7s¹. In shells that is 2, 8, 18, 32, 18, 8, 1.
How many valence electrons does francium have?
1. Francium is in group 1, and its outer shell holds 1 electron.
Where is francium on the periodic table?
In group 1, period 7, in the s-block. It is an alkali metal.
