Terbium (Tb)

Element 65 · lanthanide · group 3, period 6

Electron shells, 2 + 8 + 18 + 27 + 8 + 2. The outer shell is highlighted - it is the only one that takes part in bonding.

Terbium is element 65, a lanthanide in group 3 and period 6. Its electron configuration is [Xe] 4f9 6s2. The shells fill 2, 8, 18, 27, 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.

65 protons
2/2 valence e−
+3
f-block

Properties

Atomic number	65
Symbol	Tb
Standard atomic weight	158.93 u
Group	3
Period	6
Block	f-block
Category	lanthanide
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁹ 5s² 5p⁶ 6s²
Noble-gas notation	[Xe] 4f⁹ 6s²
Electrons per shell	2, 8, 18, 27, 8, 2
Valence electrons	2 or 2
Common ionic charge	+3
Electronegativity (Pauling)	1.1
Protons / electrons	65 / 65

Electron configuration of terbium

Orbitals fill from the lowest energy upward. Writing that out for terbium gives 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁹ 5s² 5p⁶ 6s², which is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f9 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] 4f⁹ 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	9	14
5s	2	2
5p	6	6
6s	2	2

Terbium ion charge

Terbium commonly forms ions with a charge of +3.

Common questions

How many valence electrons does terbium have?

There is no single agreed answer for terbium. 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 terbium?

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f9 5s2 5p6 6s2, or [Xe] 4f9 6s2 written from the previous noble gas. Orbitals fill lowest energy first.

What is the charge of terbium?

Terbium 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 terbium have?

A neutral terbium atom has 65 protons and 65 electrons. Its standard atomic weight is 158.93, so the most common isotope has about 94 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 65 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.