Gallium (Ga): Bohr Model, Protons, Neutrons & Electrons
Gallium is element number 31, a post-transition metal in group 13, period 4. Its atom has 31 protons, 38 neutrons and 31 electrons arranged in 4 shells: 2, 8, 18, 3.
Protons, neutrons and electrons in gallium
The atomic number of gallium is 31, so every gallium atom has 31 protons. A neutral atom has the same number of electrons, 31. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For gallium-69, that is 69 − 31 = 38 neutrons. Gallium has 2 stable isotopes, with 38, 40 neutrons.
How to draw the Bohr model of gallium
- Draw the nucleus and write 31 p⁺ and 38 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 3 electrons on it.
- Check: 2 + 8 + 18 + 3 = 31 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, 3) is the one to draw.
Electron configuration
The electron configuration of gallium is [Ar] 4s² 3d¹⁰ 4p¹. Its 3 outer electrons decide how it reacts: it tends to lose them, forming Ga³⁺ ions.
Key facts about gallium
| Symbol | Ga |
|---|---|
| Atomic number | 31 |
| Relative atomic mass | 69.723 |
| Group · period · block | group 13 · period 4 · p-block |
| Type | Post-transition Metal |
| State at 25 °C | solid |
| Electron shells | 2, 8, 18, 3 |
| Electron configuration | [Ar] 4s² 3d¹⁰ 4p¹ |
| Valence electrons | 3 |
| Common ion | Ga³⁺ |
| Electronegativity (Pauling) | 1.81 |
| First ionisation energy | 6.00 eV (579 kJ/mol) |
| Atomic radius (empirical) | 130 pm |
Where gallium sits on the periodic table
Frequently asked questions
How many protons, neutrons and electrons does gallium have?
Gallium has 31 protons and 31 electrons (atomic number 31). Its most common isotope, gallium-69, has 69 − 31 = 38 neutrons.
What is the electron configuration of gallium?
[Ar] 4s² 3d¹⁰ 4p¹. In shells that is 2, 8, 18, 3.
How many valence electrons does gallium have?
3. Gallium is in group 13, and its outer shell holds 3 electrons.
Where is gallium on the periodic table?
In group 13, period 4, in the p-block. It is a post-transition metal.
