Lawrencium at a glance
- Atomic number
- 103
- Symbol
- Lr
- Atomic mass
- 266 u
- Category
- Actinide
- Period
- 7
- Electron configuration
- [Rn] 5f 14 7s 2 7p 1
- State at 25 °C
- Solid
- Melting point
- 1627 °C
- Boiling point
- n/a
- Density
- 15.6 g/cm³
- Electronegativity
- 1.3
- 1st ionization energy
- 479 kJ/mol
- Oxidation states
- +3
- Discovered
- 1961
Atomic structure
A neutral lawrencium atom has 103 protons and 103 electrons, and its most common isotope carries about 163 neutrons. One atom weighs about 4.42 × 10⁻²⁵ kg, so a mole of lawrencium (6.022 × 10²³ atoms) weighs 266 g. That nucleus holds 1.58 neutrons for every proton, typical of heavy nuclei, which need extra neutrons to hold together against the protons' repulsion. The electrons fill 7 shells (K 2, L 8, M 18, N 32, O 32, P 8, Q 3), which gives the configuration [Rn] 5f 14 7s 2 7p 1. 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. Its configuration breaks the simple filling order: one electron moves so that a subshell becomes half-full or full, which is more stable. All of its isotopes are radioactive, so any lawrencium on Earth is either freshly made or part of a decay chain.
Physical properties
At room temperature (25 °C) lawrencium is a solid. It melts at about 1627 °C; its boiling point has not been measured. It stays solid in molten iron (1538 °C) but would melt in a welding arc. Its density is 15.6 g/cm³ (predicted), 15.6 times as dense as water.
Chemical behaviour
Its electronegativity is 1.3 on the Pauling scale. Pulling off its outermost electron takes 479 kJ/mol. A bond between lawrencium and chlorine would be mostly ionic, with an electronegativity difference of 1.9. Its common oxidation states are +3, so in compounds you will usually meet it as Lr³⁺. It shares much of its chemistry with the other actinides, especially its neighbours Mendelevium and Nobelium. Handle with care: as a pure element it is radioactive.
Where it comes from
It does not occur in nature in useful amounts; it is made in nuclear reactors or particle accelerators. It was first made at Berkeley by fusing californium with boron nuclei. Its longest-lived known isotope is Lr-266, about 11 hours. It was first identified in 1961, making it the 103rd element to be discovered (counting the 11 known since antiquity together).