Element 90 · Thorium (Th)

Thorium Bohr model: diagram and electrons per shell

The thorium Bohr model shows a thorium atom (Th) as a small nucleus with its electrons circling it in 7 shells: 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O, 10 in shell P and 2 in shell Q. This page has a rotating 3D thorium Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the thorium Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of thorium (Th), a simplified picture of a single thorium atom. Its nucleus holds 90 protons, and a neutral thorium atom has 90 electrons, arranged around it in 7 shells (2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O, 10 in shell P and 2 in shell Q).

Th K · 21s² L · 82s² 2p⁶ M · 183s² 3p⁶ 3d¹⁰ N · 324s² 4p⁶ 4d¹⁰ 4f¹⁴ O · 185s² 5p⁶ 5d¹⁰ P · 106s² 6p⁶ 6d² Q · 27s²

Thorium Bohr model diagram

Bohr model diagram of thorium: a nucleus of 90 protons with 90 electrons on 7 shells, 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O, 10 in shell P and 2 in shell Q, each ring labelled with its shell letter. — The thorium 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, 18 in shell M, 32 in shell N, 18 in shell O, 10 in shell P and 2 in shell Q).

Thorium electrons per shell

A neutral thorium atom has 90 electrons, one for each of its 90 protons. They fill the shells from the nucleus outwards: 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O, 10 in shell P and 2 in shell Q.

Electrons in each shell of the thorium 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	18	18	3s² 3p⁶ 3d¹⁰
N	4	32	32	4s² 4p⁶ 4d¹⁰ 4f¹⁴
O	5	18	50	5s² 5p⁶ 5d¹⁰
P	6	10	72	6s² 6p⁶ 6d²
Q	7	2	98	7s²

How the thorium Bohr model builds up, shell by shell

Watch the thorium 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, 18 in shell M, 32 in shell N, 18 in shell O, 10 in shell P and 2 in shell Q) as it forms.

Animation of the thorium Bohr model being built: a nucleus of 90 protons appears first, then each shell grows in around it and takes its electrons, giving 90 electrons on 7 shells (2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O, 10 in shell P and 2 in shell Q). — The thorium 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, 18 in shell M, 32 in shell N, 18 in shell O, 10 in shell P and 2 in shell Q. Protons are red, neutrons yellow and electrons blue.

How to draw the thorium Bohr model

Find the atomic number. Thorium has atomic number 90, so a neutral atom has 90 protons and 90 electrons.
Draw the nucleus. Put a circle in the centre and write Th in it. The 90 protons sit there with the neutrons.
Draw the shells. Sketch 7 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, 18 in shell M, 32 in shell N, 18 in shell O, 10 in shell P and 2 in shell Q.
Check the total. 2 + 8 + 18 + 32 + 18 + 10 + 2 = 90, the atomic number, so every electron is accounted for.

Atomic data for the thorium Bohr model

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

Identity

Symbol: Th
Atomic number: 90
Atomic mass: 232.0377 u
Family: Actinides
Position: period 7 of the f-block
Block: f-block

Electron configuration

Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 6d²
Shorthand: [Rn] 6d² 7s²
Electrons per shell: 2, 8, 18, 32, 18, 10, 2
Outer-shell electrons: 2 in shell Q

Ionisation energies

I₁: 587
I₂: 1110
I₃: 1930
I₄: 2780

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

Atomic radii

Empirical (pm): 180
Covalent (pm): 175

Electronegativity and electron affinity

Electronegativity (Pauling): 1.3
Electron affinity (kJ/mol): 112.72

Oxidation states

Charges the element commonly takes in compounds.

Physical properties, abundance and history of thorium

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

Physical properties

Phase at room conditions: Solid
Appearance: Silvery, often with black tarnish
Melting point: 1749.85°C (2023 K)
Boiling point: 4787.85°C (5061 K)
Density: 11.724 g/cm³
Specific heat (J/g·K): 0.118
Molar heat capacity (J/mol·K): 26.23
Heat of fusion (kJ/mol): 16.11
Heat of vaporisation (kJ/mol): 513.7

Abundance

Earth's crust (mg/kg): 9.6
Oceans (mg/L): 0

Discovery

Discovered by: Jöns Jakob Berzelius
Year: 1829

Common compounds

Thorium Th
THORIUM OXIDE (ThO2) O2Th
Thorium nitrate N4O12Th
Thorium tetrachloride Cl4Th
Thorium-230 Th
Thorium-228 Th
Thorium-227 Th
Thorium fluoride (ThF4), (T-4)- F4Th

Compounds listed in the PubChem database.

Main isotopes of thorium

Isotopes of thorium share the same 90 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of thorium: mass number, abundance, half-life and decay
Mass number	Natural abundance	Half-life	Decay
227	–	18.693 d	α
228	–	1.913 y	α, 20O
229	–	7.916 ky	α
230	0.02 %	75.4 ky	α, SF, 24Ne
232	99.98 %	14 Gy	α, SF, 26Ne, 2β⁻
234	–	24.107 d	β⁻, α

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

More about thorium

Thorium on the periodic table – properties, isotopes, uses and the full thorium page.
Actinides – all actinide elements and their trends.
Bohr model of every element – the Bohr model of all 118 elements.