Molybdenum (Mo): electron configuration, atomic mass and facts
Molybdenum (Mo) is element 42 of the periodic table, a transition metal in period 5, group 6. Its electron configuration is [Kr] 4d5 5s1, with electrons arranged in shells 2, 8, 18, 13, 1, and its standard atomic weight is 95.95 u.
▶ Watch Molybdenum’s electrons orbit in the interactive periodic tableMolybdenum at a glance
| Symbol | Mo |
|---|---|
| Atomic number | 42 |
| Atomic mass | 95.95 u |
| Category | Transition metal |
| Group | 6 |
| Period | 5 |
| Block | d-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d5 5s1 |
| Noble-gas shorthand | [Kr] 4d5 5s1 |
| Electrons per shell | 2, 8, 18, 13, 1 |
| Electronegativity (Pauling) | 2.16 |
| State at 20 °C | solid |
Where is Molybdenum on the periodic table?
Molybdenum is in period 5, group 6, in the d-block. The period number matches its 5 electron shells, and the block names the subshell its last electrons fill. In the same group, Chromium sits directly above it and Tungsten sits directly below it. Elements in the same column of the d-block often have similar chemistry.
How to work out the electron configuration of Molybdenum
Put 42 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20), 3d¹⁰ (30), 4p⁶ (36), 5s² (38), 4d⁴ (42). Molybdenum is one of the exceptions to this filling order: experiments show its ground state is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁵ rather than 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁴, because the neighbouring subshells are so close in energy and a half-filled or completely filled d subshell is extra stable. In shorthand, [Kr] stands for the 36 electrons of krypton, giving [Kr] 4d⁵ 5s¹.
How electronegative is Molybdenum?
Molybdenum has a Pauling electronegativity of 2.16, ranking 26 of the 100 elements with a known value (fluorine is highest at 3.98). That is in the middle of the range.
Frequently asked questions
What is the electron configuration of Molybdenum?
The electron configuration of Molybdenum (Mo) is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d5 5s1. In noble-gas shorthand it is written [Kr] 4d5 5s1.
How many electrons does Molybdenum have in each shell?
Molybdenum has 42 electrons arranged in shells as 2, 8, 18, 13, 1.
What is the atomic mass of Molybdenum?
The standard atomic weight of Molybdenum is 95.95 u, so one mole of Molybdenum atoms has a mass of about 95.95 g.
Is Molybdenum a metal?
Yes. Molybdenum is a transition metal.
Explore nearby elements
More transition metals: Yttrium, Zirconium, Niobium, Technetium, Ruthenium, Rhodium. See all elements on the periodic table.