Indium (In): Bohr Model, Protons, Neutrons & Electrons
Indium is element number 49, a post-transition metal in group 13, period 5. Its atom has 49 protons, 66 neutrons and 49 electrons arranged in 5 shells: 2, 8, 18, 18, 3.
Protons, neutrons and electrons in indium
The atomic number of indium is 49, so every indium atom has 49 protons. A neutral atom has the same number of electrons, 49. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For indium-115, that is 115 − 49 = 66 neutrons. Indium has 2 stable isotopes, with 64, 66 neutrons.
How to draw the Bohr model of indium
- Draw the nucleus and write 49 p⁺ and 66 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 18 electrons on it.
- Draw the fifth shell and put 3 electrons on it.
- Check: 2 + 8 + 18 + 18 + 3 = 49 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, 18, 3) is the one to draw.
Electron configuration
The electron configuration of indium is [Kr] 5s² 4d¹⁰ 5p¹. Its 3 outer electrons decide how it reacts: it tends to lose them, forming In³⁺ ions.
Key facts about indium
| Symbol | In |
|---|---|
| Atomic number | 49 |
| Relative atomic mass | 114.82 |
| Group · period · block | group 13 · period 5 · p-block |
| Type | Post-transition Metal |
| State at 25 °C | solid |
| Electron shells | 2, 8, 18, 18, 3 |
| Electron configuration | [Kr] 5s² 4d¹⁰ 5p¹ |
| Valence electrons | 3 |
| Common ion | In³⁺ |
| Electronegativity (Pauling) | 1.78 |
| First ionisation energy | 5.79 eV (559 kJ/mol) |
| Atomic radius (empirical) | 155 pm |
Where indium sits on the periodic table
Frequently asked questions
How many protons, neutrons and electrons does indium have?
Indium has 49 protons and 49 electrons (atomic number 49). Its most common isotope, indium-115, has 115 − 49 = 66 neutrons.
What is the electron configuration of indium?
[Kr] 5s² 4d¹⁰ 5p¹. In shells that is 2, 8, 18, 18, 3.
How many valence electrons does indium have?
3. Indium is in group 13, and its outer shell holds 3 electrons.
Where is indium on the periodic table?
In group 13, period 5, in the p-block. It is a post-transition metal.
