Molybdenum (Mo)
Element 42 · transition metal · group 6, period 5
Molybdenum is element 42, a transition metal in group 6 and period 5. Its electron configuration is [Kr] 4d5 5s1. The shells fill 2, 8, 18, 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 +6, +4.
- 42 protons
- 1/6 valence e−
- +6, +4
- d-block
Properties
| Atomic number | 42 |
|---|---|
| Symbol | Mo |
| Standard atomic weight | 95.95 u |
| Group | 6 |
| Period | 5 |
| Block | d-block |
| Category | transition metal |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d5 5s1 |
| Noble-gas notation | [Kr] 4d5 5s1 |
| Electrons per shell | 2, 8, 18, 13, 1 |
| Valence electrons | 1 or 6 |
| Common ionic charge | +6, +4 |
| Electronegativity (Pauling) | 2.16 |
| Protons / electrons | 42 / 42 |
Electron configuration of molybdenum
Orbitals fill from the lowest energy upward. Writing that out for molybdenum gives 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d5 5s1, which is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d5 5s1 in plain text.
Everything up to Kr is the same as in that noble gas, so it is usually abbreviated to [Kr] 4d5 5s1. 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 | 10 | 10 |
| 4s | 2 | 2 |
| 4p | 6 | 6 |
| 4d | 5 | 10 |
| 5s | 1 | 2 |
Molybdenum ion charge
Molybdenum commonly forms ions with a charge of +6, +4.
Common questions
How many valence electrons does molybdenum have?
There is no single agreed answer for molybdenum. 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 molybdenum?
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d5 5s1, or [Kr] 4d5 5s1 written from the previous noble gas. Orbitals fill lowest energy first, but molybdenum 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 molybdenum?
Molybdenum commonly forms ions with a charge of +6, +4. Transition metals have several accessible oxidation states, which is why more than one charge is listed.
How many protons, electrons and neutrons does molybdenum have?
A neutral molybdenum atom has 42 protons and 42 electrons. Its standard atomic weight is 95.95, so the most common isotope has about 54 neutrons.
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