Thulium (Tm)

Element 69 · lanthanide · group 3, period 6

Electron shells, 2 + 8 + 18 + 31 + 8 + 2. The outer shell is highlighted - it is the only one that takes part in bonding.

Thulium is element 69, a lanthanide in group 3 and period 6. Its electron configuration is [Xe] 4f13 6s2. The shells fill 2, 8, 18, 31, 8, 2. The f-block elements draw on three subshells, so a single valence count is not meaningful for them. It commonly forms ions with a charge of +3.

69 protons
2/2 valence e−
+3
f-block

Properties

Atomic number	69
Symbol	Tm
Standard atomic weight	168.93 u
Group	3
Period	6
Block	f-block
Category	lanthanide
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹³ 5s² 5p⁶ 6s²
Noble-gas notation	[Xe] 4f¹³ 6s²
Electrons per shell	2, 8, 18, 31, 8, 2
Valence electrons	2 or 2
Common ionic charge	+3
Electronegativity (Pauling)	1.25
Protons / electrons	69 / 69

Electron configuration of thulium

Orbitals fill from the lowest energy upward. Writing that out for thulium gives 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹³ 5s² 5p⁶ 6s², which is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f13 5s2 5p6 6s2 in plain text.

Everything up to Xe is the same as in that noble gas, so it is usually abbreviated to [Xe] 4f¹³ 6s². The part outside the bracket is what does the chemistry.

Subshell	Electrons	Capacity
1s	2	2
2s	2	2
2p	6	6
3s	2	2
3p	6	6
3d	10	10
4s	2	2
4p	6	6
4d	10	10
4f	13	14
5s	2	2
5p	6	6
6s	2	2

Thulium ion charge

Thulium commonly forms ions with a charge of +3.

Common questions

How many valence electrons does thulium have?

There is no single agreed answer for thulium. The f-block elements draw on three subshells, so a single valence count is not meaningful for them. Check which convention your course uses before answering.

What is the electron configuration of thulium?

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f13 5s2 5p6 6s2, or [Xe] 4f13 6s2 written from the previous noble gas. Orbitals fill lowest energy first.

What is the charge of thulium?

Thulium commonly forms ions with a charge of +3. Transition metals have several accessible oxidation states, which is why more than one charge is listed.

How many protons, electrons and neutrons does thulium have?

A neutral thulium atom has 69 protons and 69 electrons. Its standard atomic weight is 168.93, so the most common isotope has about 100 neutrons.

See the ionic charge of every element →

How this page was produced. The configuration was built by filling orbitals in energy order from atomic number 69 alone, not looked up. The shell counts, the valence count and the charge all follow from it. Nothing on this page is written per element.