Element 42 · Transition metal
Molybdenum (Mo) — Element 42
Greek molybdos — lead
Molybdenum (Mo) is a transition metal in Period 5, Group 6 of the periodic table with atomic number 42, standard atomic weight 95.95 u, and ground-state electron configuration [Kr] 4d⁵ 5s¹. At standard temperature and pressure it is classified as a solid with 6 valence electrons and common oxidation states +6, +4.
High-strength steel, enzymes
What are the atomic properties and physical constants of Molybdenum?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 42
- Standard atomic mass
- 95.95 u
- Chemical family
- Transition metal
- Ground-state configuration
- [Kr] 4d⁵ 5s¹
- Electrons per shell
- 2, 8, 18, 13, 1
- Valence electrons
- 6
- Common ion charges / oxidation states
- +6, +4
- Phase at STP
- Solid
- Pauling electronegativity
- 2.16 Pauling
- First ionization energy
- 684 kJ/mol
- Atomic radius
- 190 pm
- Melting point
- 2,623 °C
- Boiling point
- 4,639 °C
- Discovery year
- 1781
- Table coordinate
- Period 5, Group 6
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Molybdenum’s shells?
A neutral Molybdenum atom contains 42 electrons distributed across 5 occupied principal energy shells ([Kr] 4d⁵ 5s¹). The table below compares Molybdenum’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in Mo | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 18 e⁻ | 18 e⁻ |
| n = 4 | N | 13 e⁻ | 32 e⁻ |
| n = 5 | O | 1 e⁻ | 50 e⁻ |
Frequently Asked Questions about Molybdenum (Mo)
What is the atomic mass and atomic number of Molybdenum (Mo)?
Molybdenum (Mo) has atomic number Z = 42 (42 protons in its nucleus) and an IUPAC standard atomic weight of 95.95 u. It sits in Period 5, Group 6 and is classified as a transition metal.
What is the ground-state electron configuration of Molybdenum?
The neutral ground-state electron configuration of Molybdenum (Z = 42) is [Kr] 4d⁵ 5s¹. Across its 5 occupied principal shells (n = 1 to n = 5), the electrons per shell are 2, 8, 18, 13, 1, with 6 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Molybdenum?
Molybdenum commonly forms +6, +4 oxidation states or ion charges in compounds. Its Pauling electronegativity is 2.16 and its first ionization energy is 684 kJ/mol.
When was Molybdenum discovered and what is it used for?
Molybdenum was discovered in 1781 (Greek molybdos — lead). High-strength steel, enzymes
How does Molybdenum compare to neighboring elements?
Other transition metal elements: