Lutetium

Lutetium (Lu) is a lanthanide with atomic number 71 and an atomic mass of 174.97. Its electron configuration is [Xe] 4f14 5d1 6s2.

Lutetium key data

Symbol	Lu
Atomic number	71
Atomic mass (standard atomic weight)	174.97
Molar mass	174.97 g/mol
Protons	71
Neutrons (most abundant isotope, lutetium-175)	104
Electrons (neutral atom)	71
Category	Lanthanide
Period	6
Group	3 or none, by convention
Block	d-block or f-block, by convention
Noble gas notation	[Xe] 4f14 5d1 6s2
Full electron configuration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d1 6s2
Electrons per shell	2, 8, 18, 32, 9, 2

Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.

Measured properties of lutetium

From PubChem, the US National Institutes of Health. Public domain. PubChem’s periodic table gives no value for the rows not shown.

Melting point	1936 K (1662.9 °C), 20th of 103 by melting point
Boiling point	3675 K (3401.9 °C), 23rd of 93 by boiling point
Density	9.84 g/cm³, 27th of 96 by density
State at room temperature	Solid
Electronegativity	1.27 (Pauling), 73rd of 95 by electronegativity
Van der Waals radius	221 pm, joint 32nd of 99 by atomic radius
First ionisation energy	5.426 eV (523.5 kJ/mol), 93rd of 102 by first ionisation energy
Common oxidation states	+3
Discovered	1907

Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.

Lutetium electron configuration

The full electron configuration of lutetium is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d1 6s2. With the noble-gas core collapsed it is [Xe] 4f14 5d1 6s2, and the outermost subshell is 6s2.

Bohr model of lutetium (Lu): a nucleus and six shells holding 2, 8, 18, 32, 9 and 2 electrons from the inside out. — Bohr model of lutetium (Lu). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Orbital box diagram of lutetium (Lu), [Xe] 4f14 5d1 6s2, with the xenon core drawn as one bar: one box per orbital, filled by Hund’s rule, showing one unpaired electron, in 5d. — Orbital diagram of lutetium (Lu). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one lutetium atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

one atom = 174.97 / (6.02214076 × 10²³)
= 2.9054 × 10⁻²² g

Atoms in one gram

atoms per gram = 6.02214076 × 10²³ / 174.97
= 3.4418 × 10²¹ atoms

Lutetium on the periodic table

Lutetium is in period 6. Tables differ on its group: some place it in group 3, in the d-block, and others in the f-block, outside the numbered groups.