Radium (Ra): Bohr Model, Protons, Neutrons & Electrons
Radium is element number 88, an alkaline earth metal in group 2, period 7. Its atom has 88 protons, 138 neutrons and 88 electrons arranged in 7 shells: 2, 8, 18, 32, 18, 8, 2.
- 88 protons
- 138 neutrons
- 88 electrons
Protons, neutrons and electrons in radium
Le atomic number of radium is 88, so every radium atom has 88 protons. A neutral atom has the same number of electrons, 88. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For radium-226, that is 226 − 88 = 138 neutrons. Every isotope of radium is radioactive; 226 is the mass number of its most stable one.
How to draw the Bohr model of radium
- Draw the nucleus and write 88 p⁺ et 138 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 2 electrons on it.
- Check: 2 + 8 + 18 + 32 + 18 + 8 + 2 = 88 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, 2) is the one to draw.
Electron configuration
The electron configuration of radium is [Rn] 7s². Its 2 outer electrons decide how it reacts: it tends to lose them, forming Ra²⁺ ions.
Key facts about radium
| Symbol | Ra |
|---|---|
| Atomic number | 88 |
| Relative atomic mass | [226] |
| Group · period · block | group 2 · period 7 · s-block |
| Type | Métal alcalino-terreux |
| State at 25 °C | solid |
| Couches électroniques | 2, 8, 18, 32, 18, 8, 2 |
| Electron configuration | [Rn] 7s² |
| Électrons de valence | 2 |
| Common ion | Ra²⁺ |
| Electronegativity (Pauling) | 0.90 |
| First ionisation energy | 5.28 eV (509 kJ/mol) |
| Atomic radius (empirical) | 215 pm |
Où radium sits on the periodic table
Foire aux questions
How many protons, neutrons and electrons does radium have?
Radium has 88 protons and 88 electrons (atomic number 88). Its most common isotope, radium-226, has 226 − 88 = 138 neutrons.
What is the electron configuration of radium?
[Rn] 7s². In shells that is 2, 8, 18, 32, 18, 8, 2.
How many valence electrons does radium have?
2. Radium is in group 2, and its outer shell holds 2 electrons.
Where is radium on the periodic table?
In group 2, period 7, in the s-block. It is an alkaline earth metal.
