Element 27 · Cobalt (Co)

Cobalt Bohr model: diagram and electrons per shell

The cobalt Bohr model shows a cobalt atom (Co) as a small nucleus with its electrons circling it in 4 shells: 2 in shell K, 8 in shell L, 15 in shell M and 2 in shell N. This page has a rotating 3D cobalt Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the cobalt Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of cobalt (Co), a simplified picture of a single cobalt atom. Its nucleus holds 27 protons, and a neutral cobalt atom has 27 electrons, arranged around it in 4 shells (2 in shell K, 8 in shell L, 15 in shell M and 2 in shell N).

Co K · 21s² L · 82s² 2p⁶ M · 153s² 3p⁶ 3d⁷ N · 24s²

Cobalt Bohr model diagram

Bohr model diagram of cobalt: a nucleus of 27 protons with 27 electrons on 4 shells, 2 in shell K, 8 in shell L, 15 in shell M and 2 in shell N, each ring labelled with its shell letter. — The cobalt Bohr model drawn flat: each ring is a shell, labelled with its letter, and every dot is an electron (2 in shell K, 8 in shell L, 15 in shell M and 2 in shell N).

Cobalt electrons per shell

A neutral cobalt atom has 27 electrons, one for each of its 27 protons. They fill the shells from the nucleus outwards: 2 in shell K, 8 in shell L, 15 in shell M and 2 in shell N.

Electrons in each shell of the cobalt Bohr model
Shell	Shell number (n)	Electrons	Most it can hold (2n²)	Subshells
K	1	2	2	1s²
L	2	8	8	2s² 2p⁶
M	3	15	18	3s² 3p⁶ 3d⁷
N	4	2	32	4s²

How the cobalt Bohr model builds up, shell by shell

Watch the cobalt Bohr model come together: the nucleus first, then each shell in turn, from the innermost outwards, with its electrons joining the ring. The legend names every shell and counts its electrons, so you can read off the arrangement (2 in shell K, 8 in shell L, 15 in shell M and 2 in shell N) as it forms.

Animation of the cobalt Bohr model being built: a nucleus of 27 protons appears first, then each shell grows in around it and takes its electrons, giving 27 electrons on 4 shells (2 in shell K, 8 in shell L, 15 in shell M and 2 in shell N). — The cobalt Bohr model built up in six seconds: the nucleus first, then each shell with its electrons, ending with 2 in shell K, 8 in shell L, 15 in shell M and 2 in shell N. Protons are red, neutrons yellow and electrons blue.

How to draw the cobalt Bohr model

Find the atomic number. Cobalt has atomic number 27, so a neutral atom has 27 protons and 27 electrons.
Draw the nucleus. Put a circle in the centre and write Co in it. The 27 protons sit there with the neutrons.
Draw the shells. Sketch 4 shells as rings around the nucleus. A shell holds at most 2n² electrons: 2 in the first, 8 in the second, 18 in the third and 32 in the fourth.
Place the electrons. Fill from the inside out: 2 in shell K, 8 in shell L, 15 in shell M and 2 in shell N.
Check the total. 2 + 8 + 15 + 2 = 27, the atomic number, so every electron is accounted for.

Atomic data for the cobalt Bohr model

The numbers behind the cobalt Bohr model, grouped by topic. Radii are in picometres (pm) and energies in kilojoules per mole (kJ/mol).

Identity

Symbol: Co
Atomic number: 27
Atomic mass: 58.9332 u
Family: Transition Metals
Position: group 9, period 4
Block: d-block

Electron configuration

Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷
Shorthand: [Ar] 3d⁷ 4s²
Electrons per shell: 2, 8, 15, 2
Outer-shell electrons: 2 in shell N

Ionisation energies

I₁: 760.4
I₂: 1648
I₃: 3232
I₄: 4950
I₅: 7670
I₆: 9840
I₇: 12440
I₈: 15230

Energy to remove each electron in turn (kJ/mol). A sharp jump means the next electron comes from an inner shell.

Atomic radii

Calculated (pm): 152
Empirical (pm): 135
Covalent (pm): 111

Electronegativity and electron affinity

Electronegativity (Pauling): 1.88
Electron affinity (kJ/mol): 63.898

Oxidation states

+2 +3

Charges the element commonly takes in compounds.

Physical properties, abundance and history of cobalt

Bulk properties of cobalt, how common it is, who discovered it and some of its compounds.

Physical properties

Phase at room conditions: Solid
Appearance: Hard lustrous gray metal
Melting point: 1494.85°C (1768 K)
Boiling point: 2926.85°C (3200 K)
Density: 8.9 g/cm³
Thermal conductivity (W/m·K): 100
Specific heat (J/g·K): 0.421
Molar heat capacity (J/mol·K): 24.81
Heat of fusion (kJ/mol): 15.48
Heat of vaporisation (kJ/mol): 389.1

Abundance

Earth's crust (mg/kg): 25
Oceans (mg/L): 0

Discovery

Discovered by: Georg Brandt
Year: 1735

Common compounds

Cobalt Co
Cobalt chloride (cocl2) Cl2Co
Hydroxocobalamin C62H89CoN13O15P
Cobalt Sulfate CoO4S
Cobalt diacetate C4H6CoO4
Cobalt(II) oxide CoO
Cobalt naphthenate C20H34CoO4
Cyanocobalamin C63H88CoN14O14P

Compounds listed in the PubChem database.

Main isotopes of cobalt

Isotopes of cobalt share the same 27 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of cobalt: mass number, abundance, half-life and decay
Mass number	Natural abundance	Half-life	Decay
55	–	17.53 h	β⁺
56	–	77.236 d	β⁺
57	–	271.811 d	EC
58	–	70.844 d	β⁺, e⁺, EC
59	100 %	stable	–
60	–	5.271 y	β⁻

α = alpha decay, β⁻ = beta-minus, β⁺ = beta-plus, EC = electron capture, SF = spontaneous fission, p / n = proton / neutron emission.

More about cobalt

Cobalt on the periodic table – properties, isotopes, uses and the full cobalt page.
Transition Metals – all transition metal elements and their trends.
Bohr model of every element – the Bohr model of all 118 elements.