LanthanideElement 68 · f-block

Erbium (Er)

Erbium (Er) is a lanthanide with atomic number 68 and a standard atomic weight of 167.26. At room temperature it is a solid that melts at 1,529 °C and boils at 2,868 °C.

68ErErbium167.26

Atomic number

protons

Atomic weight

167.26

CIAAW 2024

Melting point

1,529 °C

1,802.15 K

Boiling point

2,868 °C

3,141.15 K

Density

9.07 g/cm³

near room temperature

Electronegativity

1.24

Pauling scale

State at 25 °C

Solid

Discovered

1843

Sweden

Erbium at a glance

Identity

Symbol	Er
Atomic number (Z)	68
Atomic weight	167.26 ± 0.01 (CIAAW 2024)
Category	Lanthanide
Group	— (f-block: lanthanide series)
Period	6
Block	f-block
CAS number	7440-52-0

Atomic properties

Electron configuration	[Xe] 4f¹² 6s² Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹² 5s² 5p⁶ 6s²
Electrons per shell	2, 8, 18, 30, 8, 2
Oxidation states	+3 Less common: 0, +1, +2
Electronegativity (Pauling)	1.24
First ionisation energy	6.108 eV (589.3 kJ/mol) 2nd: 11.916 eV · 3rd: 22.7 eV
Atomic radius (empirical)	175 pm
Covalent radius	165 pm
Van der Waals radius	229 pm

Physical properties

State at 25 °C	Solid
Melting point	1,529 °C · 2,784.2 °F · 1,802.15 K
Boiling point	2,868 °C · 5,194.4 °F · 3,141.15 K
Density	9.07 g/cm³
Specific heat capacity	0.168 J/(g·K)
Crystal structure	Hexagonal

Isotopes & abundance

Natural occurrence	Primordial
Radioactive	No
Natural isotopes (abundance)	¹⁶⁶Er 33.503%, ¹⁶⁸Er 26.978%, ¹⁶⁷Er 22.869%, ¹⁷⁰Er 14.91%, ¹⁶⁴Er 1.601%, ¹⁶²Er 0.139%
Stable isotopes	6
Known isotopes	39
Abundance in Earth's crust	3.5 mg/kg
Abundance in seawater	0.00000087 mg/L

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Erbium electron configuration

Erbium has 68 electrons. Written in short form, its ground-state configuration is [Xe] 4f¹² 6s² — the electrons of the noble gas xenon, plus 4f¹² 6s².Written out in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹² 5s² 5p⁶ 6s².

4f↑↓↑↓↑↓↑↓↑↓↑↑

6s↑↓

Discovery and name

Discovered

1843 — Carl Gustaf Mosander · Sweden.

Name

Ytterby, Sweden.

Known for

Erbium-doped fibre amplifiers boost the light signals in long-distance internet cables; erbium also gives glass a pink tint.

Isotopes of erbium

Naturally occurring erbium is a mix of 6 isotopes. Each has 68 protons; they differ in the number of neutrons:

Isotope	Protons	Neutrons	Natural abundance	Stability
¹⁶⁶Er	68	98	33.503%	stable
¹⁶⁸Er	68	100	26.978%	stable
¹⁶⁷Er	68	99	22.869%	stable
¹⁷⁰Er	68	102	14.91%	stable
¹⁶⁴Er	68	96	1.601%	stable
¹⁶²Er	68	94	0.139%	stable

39 isotopes of erbium are known in our data set (half-lives as published in nuclear data tables).

Erbium and its neighbours in the lanthanide series

Neighbouring elements in the same f-block series:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Terbium	65	158.93	1,359 °C	3,230 °C	8.23 g/cm³	1.1
Dysprosium	66	162.50	1,412 °C	2,567 °C	8.55 g/cm³	1.22
Holmium	67	164.93	1,472 °C	2,700 °C	8.8 g/cm³	1.23
Erbium	68	167.26	1,529 °C	2,868 °C	9.07 g/cm³	1.24
Thulium	69	168.93	1,545 °C	1,950 °C	9.321 g/cm³	1.25
Ytterbium	70	173.05	824 °C	1,196 °C	6.9 g/cm³	1.1
Lutetium	71	174.97	1,663 °C	3,402 °C	9.84 g/cm³	1.27

Frequently asked questions

6 answers

What is the atomic mass of erbium?

The standard atomic weight of erbium is 167.26 ± 0.01 (CIAAW 2024), so one mole weighs about 167.26 grams.

How many protons, neutrons and electrons does erbium have?

A neutral erbium atom has 68 protons and 68 electrons. Its most common isotope, erbium-166, has 98 neutrons.

What is the electron configuration of erbium?

[Xe] 4f¹² 6s² (in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹² 5s² 5p⁶ 6s²).

What are the melting and boiling points of erbium?

Erbium melts at 1,529 °C (2,784.2 °F) and boils at 2,868 °C (5,194.4 °F).

Is erbium a metal?

Erbium is a metal. It is in the f-block, period 6, and is a solid at room temperature.

Who discovered erbium?

1843 — Carl Gustaf Mosander (Sweden).