---
title: "Cobalt (Co): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/cobalt.html
description: "Cobalt (Co), element 27: atomic mass 58.933, electron configuration [Ar] 3d⁷ 4s², group 9, period 4, d-block transition metal. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
27Co58.933

# Cobalt (Co) – element 27

Cobalt is a chemical element with the symbol **Co** and atomic number **27**. It is a transition metal in group 9, period 4 of the periodic table (d-block), and is a solid at room temperature.

Cobalt (Co) has atomic number 27, atomic mass 58.933 u and electron configuration [Ar] 3d7 4s2.

[Download periodic table PDF](https://www.moldraw.com/printables/periodic-table.pdf)[Open interactive periodic table](https://www.moldraw.com/tools/free-chem-tools/interactive-periodic-table.html)

## Cobalt facts

| Symbol | Co |
| --- | --- |
| Atomic number | 27 |
| Atomic mass | 58.933 u (g/mol) |
| Category | transition metal |
| Group | group 9 |
| Period | 4 |
| Block | d-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d7 |
| Noble-gas notation | [Ar] 3d7 4s2 |
| Electrons per shell | 2, 8, 15, 2 |

## Bohr model and shells

Cobalt has 27 electrons in 4 shells: 2, 8, 15, 2. Full configuration and noble-gas notation are in the table; work out any element or ion with the [electron configuration calculator](https://www.moldraw.com/tools/free-chem-tools/electron-configuration-calculator.html).

## Physical and atomic properties

| Melting point | 1768 K (1494.8 °C) |
| --- | --- |
| Boiling point | 3200 K (2926.8 °C) |
| Density | 8.9 g/cm³ |
| Electronegativity (Pauling) | 1.88 |
| Electron affinity | 63.898 kJ/mol |
| Ionization energies | 760.4, 1648, 3232 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 24.81 J/(mol·K) |
| Discovered by | Georg Brandt |

Use the atomic mass in the [molar mass calculator](https://www.moldraw.com/tools/free-chem-tools/molar-mass-calculator.html) for any formula containing Co.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of cobalt?

The atomic mass of cobalt is 58.933 u, so one mole of cobalt atoms weighs 58.933 g.

### What is the electron configuration of cobalt?

Cobalt has 27 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷, or [Ar] 3d⁷ 4s² in noble-gas notation. Electrons per shell: 2, 8, 15, 2.

### Is cobalt a metal?

Yes. Cobalt is a transition metal.

### Where is cobalt on the periodic table?

Cobalt is in group 9, period 4, in the d-block.

Data: [Periodic-Table-JSON](https://github.com/Bowserinator/Periodic-Table-JSON) (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.