---
title: "Molybdenum (Mo) — element 42"
description: "Molybdenum is element 42, symbol Mo, atomic weight 95.95. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/molybdenum/
site: "At One Place"
---

# Molybdenum (Mo)

**Molybdenum — element 42: Mo**

95.95 u · Transition metal · period 5, group 6

Molybdenum has the sixth-highest melting point of any element at 2,623 °C, and unlike tungsten it can be worked without extreme difficulty, which is why furnace interiors are built from it. Nitrogen-fixing bacteria use a molybdenum-iron cofactor to break the N≡N bond at ordinary temperature and pressure — the reaction industry needs 450 °C and 200 atmospheres to force. Its disulfide is structurally like graphite, sheets that slide over one another, and it keeps working in a vacuum where graphite fails because graphite's lubricity secretly depends on adsorbed water.

## Properties

- **Atomic number:** 42
- **Symbol:** Mo
- **Standard atomic weight:** 95.95 u
- **Category:** Transition metal
- **Group:** 6
- **Period:** 5
- **Block:** d-block
- **Electron configuration:** [Kr] 5s¹ 4d⁵
- **Electrons per shell:** 2, 8, 18, 13, 1
- **Melting point:** 2,896 K — 2622.8 °C — 4753.1 °F
- **Boiling point:** 4,912 K — 4638.9 °C — 8381.9 °F
- **Density:** 10.2 g/cm³
- **Electronegativity:** 2.16 (Pauling)
- **Oxidation states:** +6, +4, +3
- **Discovered:** 1778 by Carl Wilhelm Scheele; isolated by Peter Jacob Hjelm in 1781

## Electron configuration

- **Full:** 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁵
- **Noble gas shorthand:** [Kr] 5s¹ 4d⁵
- **Shells:** K: 2 · L: 8 · M: 18 · N: 13 · O: 1

## What it is used for

- High-strength steel for pressure vessels, gun barrels and drill pipe
- Molybdenum disulfide as a dry lubricant in vacuum and high heat
- Furnace heating elements and glass-melting electrodes
- Molybdenum-99, whose decay product runs most nuclear medicine scans
- Hydrodesulfurisation catalysts in oil refineries

> Anomalous electron configuration: [Kr] 5s¹ 4d⁵ rather than the predicted 5s² 4d⁴ — the same half-filled-subshell effect as chromium, directly above it.

## Neighbours in the table

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 40 | Zirconium | Zr | 91.222 |
| 41 | Niobium | Nb | 92.906 |
| 42 | Molybdenum ← | Mo | 95.95 |
| 43 | Technetium | Tc | [97] |
| 44 | Ruthenium | Ru | 101.07 |

## Group 6

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Molybdenum sits in group 6 with chromium, tungsten, seaborgium.

## Common questions

### What is the atomic number of molybdenum?

42. That is the number of protons in its nucleus, which is what defines the element.

### What is the symbol for molybdenum?

Mo.

### What is the electron configuration of molybdenum?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁵, or [Kr] 5s¹ 4d⁵ in noble-gas shorthand.

### What is the melting point of molybdenum?

2,896 K — 2622.8 °C — 4753.1 °F

## Related pages

- [Zirconium (Zr)](https://atoneplace.net/element/zirconium/)
- [Niobium (Nb)](https://atoneplace.net/element/niobium/)
- [Technetium (Tc)](https://atoneplace.net/element/technetium/)
- [Ruthenium (Ru)](https://atoneplace.net/element/ruthenium/)
- [Chromium (Cr)](https://atoneplace.net/element/chromium/)
- [Tungsten (W)](https://atoneplace.net/element/tungsten/)
- [Seaborgium (Sg)](https://atoneplace.net/element/seaborgium/)

## Sources

- Official vendor product documentation — At One Place (/about/)