Element 69 · Thulium (Tm)

Thulium Bohr model: diagram and electrons per shell

The thulium Bohr model shows a thulium atom (Tm) as a small nucleus with its electrons circling it in 6 shells: 2 in shell K, 8 in shell L, 18 in shell M, 31 in shell N, 8 in shell O and 2 in shell P. This page has a rotating 3D thulium Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the thulium Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of thulium (Tm), a simplified picture of a single thulium atom. Its nucleus holds 69 protons, and a neutral thulium atom has 69 electrons, arranged around it in 6 shells (2 in shell K, 8 in shell L, 18 in shell M, 31 in shell N, 8 in shell O and 2 in shell P).

Tm K · 21s² L · 82s² 2p⁶ M · 183s² 3p⁶ 3d¹⁰ N · 314s² 4p⁶ 4d¹⁰ 4f¹³ O · 85s² 5p⁶ P · 26s²

Thulium Bohr model diagram

Bohr model diagram of thulium: a nucleus of 69 protons with 69 electrons on 6 shells, 2 in shell K, 8 in shell L, 18 in shell M, 31 in shell N, 8 in shell O and 2 in shell P, each ring labelled with its shell letter. — The thulium 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, 31 in shell N, 8 in shell O and 2 in shell P).

Thulium electrons per shell

A neutral thulium atom has 69 electrons, one for each of its 69 protons. They fill the shells from the nucleus outwards: 2 in shell K, 8 in shell L, 18 in shell M, 31 in shell N, 8 in shell O and 2 in shell P.

Electrons in each shell of the thulium 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	31	32	4s² 4p⁶ 4d¹⁰ 4f¹³
O	5	8	50	5s² 5p⁶
P	6	2	72	6s²

How the thulium Bohr model builds up, shell by shell

Watch the thulium 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, 31 in shell N, 8 in shell O and 2 in shell P) as it forms.

Animation of the thulium Bohr model being built: a nucleus of 69 protons appears first, then each shell grows in around it and takes its electrons, giving 69 electrons on 6 shells (2 in shell K, 8 in shell L, 18 in shell M, 31 in shell N, 8 in shell O and 2 in shell P). — The thulium 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, 31 in shell N, 8 in shell O and 2 in shell P. Protons are red, neutrons yellow and electrons blue.

How to draw the thulium Bohr model

Find the atomic number. Thulium has atomic number 69, so a neutral atom has 69 protons and 69 electrons.
Draw the nucleus. Put a circle in the centre and write Tm in it. The 69 protons sit there with the neutrons.
Draw the shells. Sketch 6 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, 31 in shell N, 8 in shell O and 2 in shell P.
Check the total. 2 + 8 + 18 + 31 + 8 + 2 = 69, the atomic number, so every electron is accounted for.

Atomic data for the thulium Bohr model

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

Identity

Symbol: Tm
Atomic number: 69
Atomic mass: 168.9342 u
Family: Lanthanides
Position: period 6 of the f-block
Block: f-block

Electron configuration

Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹³
Shorthand: [Xe] 4f¹³ 6s²
Electrons per shell: 2, 8, 18, 31, 8, 2
Outer-shell electrons: 2 in shell P

Ionisation energies

I₁: 596.7
I₂: 1160
I₃: 2285
I₄: 4120

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): 222
Empirical (pm): 175
Covalent (pm): 164

Electronegativity and electron affinity

Electronegativity (Pauling): 1.25
Electron affinity (kJ/mol): 99

Oxidation states

Charges the element commonly takes in compounds.

Physical properties, abundance and history of thulium

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

Physical properties

Phase at room conditions: Solid
Appearance: Silvery gray
Melting point: 1544.85°C (1818 K)
Boiling point: 1949.85°C (2223 K)
Density: 9.32 g/cm³
Specific heat (J/g·K): 0.16
Molar heat capacity (J/mol·K): 27.03
Heat of vaporisation (kJ/mol): 232

Abundance

Earth's crust (mg/kg): 0.52
Oceans (mg/L): 0

Discovery

Discovered by: Per Teodor Cleve
Year: 1879

Common compounds

Thulium Tm
Thulium trichloride Cl3Tm
Thulium nitride (TmN) NTm
Thulium iodide (TmI3) I3Tm
Acetic acid, thulium(3+) salt (3:1) C6H9O6Tm
Thulium citrate C6H5O7Tm
Thulium arsenide (TmAs) AsTm
Thulium fluoride (TmF3) F3Tm

Compounds listed in the PubChem database.

Main isotopes of thulium

Isotopes of thulium share the same 69 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of thulium: mass number, abundance, half-life and decay
Mass number	Natural abundance	Half-life	Decay
167	–	9.25 d	EC
168	–	93.1 d	β⁺, β⁻
169	100 %	stable	–
170	–	128.6 d	β⁻, EC
171	–	1.92 y	β⁻
172	–	63.6 h	β⁻

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

More about thulium

Thulium on the periodic table – properties, isotopes, uses and the full thulium page.
Lanthanides – all lanthanide elements and their trends.
Bohr model of every element – the Bohr model of all 118 elements.