Lutetium at a glance
- Atomic number
- 71
- Symbol
- Lu
- Atomic mass
- 174.97 u
- Category
- Lanthanide
- Period
- 6
- Electron configuration
- [Xe] 4f 14 5d 1 6s 2
- State at 25 °C
- Solid
- Melting point
- 1652 °C
- Boiling point
- 3402 °C
- Density
- 9.84 g/cm³
- Electronegativity
- 1.27
- 1st ionization energy
- 524 kJ/mol
- Oxidation states
- +3
- Discovered
- 1907
Atomic structure
A neutral lutetium atom has 71 protons and 71 electrons, and its most common isotope carries about 104 neutrons. One atom weighs about 2.91 × 10⁻²⁵ kg, so a mole of lutetium (6.022 × 10²³ atoms) weighs 174.97 g. That nucleus holds 1.46 neutrons for every proton, typical of heavy nuclei, which need extra neutrons to hold together against the protons' repulsion. The electrons fill 6 shells (K 2, L 8, M 18, N 32, O 9, P 2), which gives the configuration [Xe] 4f 14 5d 1 6s 2. As a f-block element, both its outer s electrons and its inner f electrons can take part in bonding, which is why it shows more than one oxidation state. It has only one stable isotope, Lu-175, plus the long-lived Lu-176. No other element has a stable isotope with mass number 175, so Lu-175 has no stable isobars; its neighbours on that line decay into it or away from it.
Physical properties
At room temperature (25 °C) lutetium is a solid. It melts at 1652 °C and boils at 3402 °C, so it stays liquid across a 1750-degree range. It stays solid in molten iron (1538 °C) but would melt in a welding arc. Its density is 9.84 g/cm³, 9.84 times as dense as water. Its atoms have a radius of about 175 pm (Ytterbium next door is 175 pm). In the solid, its atoms pack into a hexagonal close-packed lattice.
Chemical behaviour
Its electronegativity is 1.27 on the Pauling scale. Pulling off its outermost electron takes 524 kJ/mol. A bond between lutetium and chlorine would be mostly ionic, with an electronegativity difference of 1.9. It releases 33 kJ/mol when it gains an extra electron. Its common oxidation states are +3, so in compounds you will usually meet it as Lu³⁺. It shares much of its chemistry with the other lanthanides, especially its neighbours Thulium and Ytterbium.
Where it comes from
It makes up 0.8 mg/kg of Earth's crust, the 61st most abundant element there. It was first identified in 1907, making it the 85th element to be discovered (counting the 11 known since antiquity together).