Europium at a glance
- Atomic number
- 63
- Symbol
- Eu
- Atomic mass
- 151.96 u
- Category
- Lanthanide
- Period
- 6
- Electron configuration
- [Xe] 4f 7 6s 2
- State at 25 °C
- Solid
- Melting point
- 825.9 °C
- Boiling point
- 1529 °C
- Density
- 5.243 g/cm³
- Electronegativity
- 1.2
- 1st ionization energy
- 547 kJ/mol
- Oxidation states
- +3, +2
- Discovered
- 1901
Atomic structure
A neutral europium atom has 63 protons and 63 electrons, and its most common isotope carries about 89 neutrons. One atom weighs about 2.52 × 10⁻²⁵ kg, so a mole of europium (6.022 × 10²³ atoms) weighs 151.96 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 25, O 8, P 2), which gives the configuration [Xe] 4f 7 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 2 stable isotopes: Eu-151 and Eu-153. Its most common isotope, Eu-152, has the same mass number as Sm-152: isobars, nuclei of different elements with 152 nucleons each.
Physical properties
At room temperature (25 °C) europium is a solid. It melts at 825.9 °C and boils at 1529 °C, so it stays liquid across a 703-degree range. It stays solid in a hot kitchen oven but would melt in a candle flame (about 1000 °C). Its density is 5.243 g/cm³, 5.24 times as dense as water. Its atoms have a radius of about 185 pm (Samarium next door is 185 pm). In the solid, its atoms pack into a body-centred cubic lattice.
Chemical behaviour
Its electronegativity is 1.2 on the Pauling scale. Pulling off its outermost electron takes 547 kJ/mol. A bond between europium and chlorine would be mostly ionic, with an electronegativity difference of 2. Its common oxidation states are +3, +2, so in compounds you will usually meet it as Eu³⁺ and Eu²⁺. It shares much of its chemistry with the other lanthanides, especially its neighbours Promethium, Samarium, Gadolinium and Terbium.
Where it comes from
It makes up 2 mg/kg of Earth's crust, the 52nd most abundant element there. It was first identified in 1901, making it the 84th element to be discovered (counting the 11 known since antiquity together).