Chromium (Cr)
Element 24 · transition metal · group 6, period 4
Chromium is element 24, a transition metal in group 6 and period 4. Its electron configuration is [Ar] 3d5 4s1. The shells fill 2, 8, 13, 1. Courses differ here. Counting only the outer s subshell gives 1; counting the inner d subshell with it gives 6, which is the group number. It commonly forms ions with a charge of +3, +6, +2.
- 24 protons
- 1/6 valence e−
- +3, +6, +2
- d-block
Properties
| Atomic number | 24 |
|---|---|
| Symbol | Cr |
| Standard atomic weight | 51.996 u |
| Group | 6 |
| Period | 4 |
| Block | d-block |
| Category | transition metal |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d5 4s1 |
| Noble-gas notation | [Ar] 3d5 4s1 |
| Electrons per shell | 2, 8, 13, 1 |
| Valence electrons | 1 or 6 |
| Common ionic charge | +3, +6, +2 |
| Electronegativity (Pauling) | 1.66 |
| Protons / electrons | 24 / 24 |
Electron configuration of chromium
Orbitals fill from the lowest energy upward. Writing that out for chromium gives 1s2 2s2 2p6 3s2 3p6 3d5 4s1, which is 1s2 2s2 2p6 3s2 3p6 3d5 4s1 in plain text.
Everything up to Ar is the same as in that noble gas, so it is usually abbreviated to [Ar] 3d5 4s1. The part outside the bracket is what does the chemistry.
| Subshell | Electrons | Capacity |
|---|---|---|
| 1s | 2 | 2 |
| 2s | 2 | 2 |
| 2p | 6 | 6 |
| 3s | 2 | 2 |
| 3p | 6 | 6 |
| 3d | 5 | 10 |
| 4s | 1 | 2 |
Chromium ion charge
Chromium commonly forms ions with a charge of +3, +6, +2.
Common questions
How many valence electrons does chromium have?
There is no single agreed answer for chromium. Courses differ here. Counting only the outer s subshell gives 1; counting the inner d subshell with it gives 6, which is the group number. Check which convention your course uses before answering.
What is the electron configuration of chromium?
1s2 2s2 2p6 3s2 3p6 3d5 4s1, or [Ar] 3d5 4s1 written from the previous noble gas. Orbitals fill lowest energy first, but chromium is one of the elements that breaks that order - a half-filled or filled d subshell is stable enough to be worth borrowing an s electron for.
What is the charge of chromium?
Chromium commonly forms ions with a charge of +3, +6, +2. Transition metals have several accessible oxidation states, which is why more than one charge is listed.
How many protons, electrons and neutrons does chromium have?
A neutral chromium atom has 24 protons and 24 electrons. Its standard atomic weight is 51.996, so the most common isotope has about 28 neutrons.
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