Cerium at a glance
- Atomic number
- 58
- Symbol
- Ce
- Atomic mass
- 140.12 u
- Category
- Lanthanide
- Period
- 6
- Electron configuration
- [Xe] 4f 1 5d 1 6s 2
- State at 25 °C
- Solid
- Melting point
- 794.9 °C
- Boiling point
- 3443 °C
- Density
- 6.77 g/cm³
- Electronegativity
- 1.12
- 1st ionization energy
- 534 kJ/mol
- Oxidation states
- +3, +4
- Discovered
- 1803
Atomic structure
A neutral cerium atom has 58 protons and 58 electrons, and its most common isotope carries about 82 neutrons. One atom weighs about 2.33 × 10⁻²⁵ kg, so a mole of cerium (6.022 × 10²³ atoms) weighs 140.12 g. That nucleus holds 1.41 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 19, O 9, P 2), which gives the configuration [Xe] 4f 1 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. Its configuration breaks the simple filling order: one electron moves so that a subshell becomes half-full or full, which is more stable. It has 4 stable isotopes: Ce-136, Ce-138, Ce-140 and Ce-142. No other element has a stable isotope with mass number 140, so Ce-140 has no stable isobars; its neighbours on that line decay into it or away from it.
Physical properties
At room temperature (25 °C) cerium is a solid. It melts at 794.9 °C and boils at 3443 °C, so it stays liquid across a 2648-degree range. It stays solid in a hot kitchen oven but would melt in a candle flame (about 1000 °C). Its density is 6.77 g/cm³, 6.77 times as dense as water. Its atoms have a radius of about 185 pm (Lanthanum next door is 195 pm). In the solid, its atoms pack into a face-centred cubic lattice.
Chemical behaviour
Its electronegativity is 1.12 on the Pauling scale. Pulling off its outermost electron takes 534 kJ/mol. A bond between cerium and chlorine would be mostly ionic, with an electronegativity difference of 2. It releases 55 kJ/mol when it gains an extra electron. Its common oxidation states are +3, +4, so in compounds you will usually meet it as Ce³⁺ and Ce⁴⁺. It shares much of its chemistry with the other lanthanides, especially its neighbours Lanthanum, Praseodymium and Neodymium.
Where it comes from
It makes up 66.5 mg/kg of Earth's crust, the 25th most abundant element there. It was first identified in 1803, making it the 39th element to be discovered (counting the 11 known since antiquity together).