ActinideElement 103 · f-block

Lawrencium (Lr)

Lawrencium (Lr) is an actinide with atomic number 103; its most stable known isotope has mass number 266. At room temperature it is a solid that melts at 1,627 °C (estimated).

103LrLawrencium[266]

Atomic number

103

protons

Atomic weight

[266]

most stable isotope

Melting point

1,627 °C

estimated

Boiling point

—

Density

15.6 g/cm³

predicted

Electronegativity

1.3

Pauling scale

State at 25 °C

Solid

Discovered

1961–1971

United States / USSR

Lawrencium at a glance

Identity

Symbol	Lr
Atomic number (Z)	103
Atomic weight	[266] mass number of the most stable isotope
Category	Actinide
Group	— (f-block: actinide series)
Period	7
Block	f-block
CAS number	22537-19-5

Atomic properties

Electron configuration	[Rn] 5f¹⁴ 7s² 7p¹ Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹⁴ 6s² 6p⁶ 7s² 7p¹
Electrons per shell	2, 8, 18, 32, 32, 8, 3
Oxidation states	+3
Electronegativity (Pauling)	1.3
First ionisation energy	4.96 eV (478.6 kJ/mol) 2nd: 14.54 eV · 3rd: 21.8 eV
Covalent radius	161 pm
Van der Waals radius	246 pm

Physical properties

State at 25 °C	Solid
Melting point	1,627 °C · 2,960.6 °F · 1,900.15 K estimated
Density	15.6 g/cm³ (predicted)

Isotopes & abundance

Natural occurrence	Synthetic
Radioactive	Yes
Most stable isotope	²⁶⁶Lr — half-life 22 h
Known isotopes	16

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

Lawrencium electron configuration

Lawrencium has 103 electrons. Written in short form, its ground-state configuration is [Rn] 5f¹⁴ 7s² 7p¹ — the electrons of the noble gas radon, plus 5f¹⁴ 7s² 7p¹.Written out in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹⁴ 6s² 6p⁶ 7s² 7p¹.

An exception to the filling rule. The simple aufbau (Madelung) order predicts 6d¹, 7p⁰, but lawrencium actually has 6d⁰, 7p¹. Half-filled and filled subshells, and the close energies of the outer orbitals, make this arrangement more stable.

5f↑↓↑↓↑↓↑↓↑↓↑↓↑↓

7s↑↓

7p↑

Discovery and name

Discovered

1961–1971 — Albert Ghiorso and co-workers (Berkeley); Georgy Flerov's group (Dubna) · United States / USSR.

Name

Ernest Lawrence, inventor of the cyclotron.

Known for

The last actinide. Experiments suggest its electron configuration may end in 7p rather than 6d.

Isotopes of lawrencium

Lawrencium has no stable isotopes and does not occur naturally in significant amounts. Its longest-lived known isotope is:

Isotope	Protons	Neutrons	Half-life
²⁶⁶Lr	103	163	22 h

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

Lawrencium and its neighbours in the actinide series

Neighbouring elements in the same f-block series:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Fermium	100	[257]	1,527 °C (est.)	—	9.7 g/cm³ (pred.)	1.3
Mendelevium	101	[258]	827 °C (est.)	—	10.3 g/cm³ (pred.)	1.3
Nobelium	102	[259]	827 °C (est.)	—	9.9 g/cm³ (pred.)	1.3
Lawrencium	103	[266]	1,627 °C (est.)	—	15.6 g/cm³ (pred.)	1.3

Frequently asked questions

6 answers

What is the atomic mass of lawrencium?

Lawrencium has no stable isotopes, so it has no standard atomic weight. Periodic tables show [266], the mass number of its most stable known isotope.

How many protons, neutrons and electrons does lawrencium have?

A neutral lawrencium atom has 103 protons and 103 electrons. Its most stable isotope, lawrencium-266, has 163 neutrons.

What is the electron configuration of lawrencium?

[Rn] 5f¹⁴ 7s² 7p¹ (in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹⁴ 6s² 6p⁶ 7s² 7p¹).

What are the melting and boiling points of lawrencium?

Lawrencium melts at 1,627 °C (2,960.6 °F) (estimated).

Is lawrencium a metal?

Lawrencium is a metal. It is in the f-block, period 7, and is a solid at room temperature.

Who discovered lawrencium?

1961–1971 — Albert Ghiorso and co-workers (Berkeley); Georgy Flerov's group (Dubna) (United States / USSR).