Chromium (Cr): Bohr Model, Protons, Neutrons & Electrons
Chromium is element number 24, a transition metal in group 6, period 4. Its atom has 24 protons, 28 neutrons and 24 electrons arranged in 4 shells: 2, 8, 13, 1.
Protons, neutrons and electrons in chromium
The atomic number of chromium is 24, so every chromium atom has 24 protons. A neutral atom has the same number of electrons, 24. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For chromium-52, that is 52 − 24 = 28 neutrons. Chromium has 4 stable isotopes, with 26, 28, 29, 30 neutrons.
How to draw the Bohr model of chromium
- Draw the nucleus and write 24 p⁺ and 28 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 13 electrons on it.
- Draw the fourth shell and put 1 electron on it.
- Check: 2 + 8 + 13 + 1 = 24 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, 13, 1) is the one to draw.
Electron configuration
The electron configuration of chromium is [Ar] 4s¹ 3d⁵. As a transition metal it fills an inner d-subshell, and its common ion is Cr³⁺.
Key facts about chromium
| Symbol | Cr |
|---|---|
| Atomic number | 24 |
| Relative atomic mass | 51.996 |
| Group · period · block | group 6 · period 4 · d-block |
| Type | Transition Metal |
| State at 25 °C | solid |
| Electron shells | 2, 8, 13, 1 |
| Electron configuration | [Ar] 4s¹ 3d⁵ |
| Valence electrons | varies (outer shell: 1) |
| Common ion | Cr³⁺ |
| Electronegativity (Pauling) | 1.66 |
| First ionisation energy | 6.77 eV (653 kJ/mol) |
| Atomic radius (empirical) | 140 pm |
Where chromium sits on the periodic table
Frequently asked questions
How many protons, neutrons and electrons does chromium have?
Chromium has 24 protons and 24 electrons (atomic number 24). Its most common isotope, chromium-52, has 52 − 24 = 28 neutrons.
What is the electron configuration of chromium?
[Ar] 4s¹ 3d⁵. In shells that is 2, 8, 13, 1.
How many valence electrons does chromium have?
Chromium is a transition metal, so its valence electrons are spread over two shells; its outermost shell holds 1.
Where is chromium on the periodic table?
In group 6, period 4, in the d-block. It is a transition metal.
