Erbium at a glance
- Atomic number
- 68
- Symbol
- Er
- Atomic mass
- 167.26 u
- Category
- Lanthanide
- Period
- 6
- Electron configuration
- [Xe] 4f 12 6s 2
- State at 25 °C
- Solid
- Melting point
- 1529 °C
- Boiling point
- 2868 °C
- Density
- 9.066 g/cm³
- Electronegativity
- 1.24
- 1st ionization energy
- 589 kJ/mol
- Oxidation states
- +3
- Discovered
- 1843
Atomic structure
A neutral erbium atom has 68 protons and 68 electrons, and its most common isotope carries about 94 neutrons. One atom weighs about 2.78 × 10⁻²⁵ kg, so a mole of erbium (6.022 × 10²³ atoms) weighs 167.26 g. That nucleus holds 1.38 neutrons for every proton. The electrons fill 6 shells (K 2, L 8, M 18, N 30, O 8, P 2), which gives the configuration [Xe] 4f 12 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 6 stable isotopes: Er-162, Er-164, Er-166, Er-167, Er-168 and Er-170. Its most common isotope, Er-162, has the same mass number as Dy-162: isobars, nuclei of different elements with 162 nucleons each.
Physical properties
At room temperature (25 °C) erbium is a solid. It melts at 1529 °C and boils at 2868 °C, so it stays liquid across a 1339-degree range. It stays solid in a candle flame (about 1000 °C) but would melt in molten iron (1538 °C). Its density is 9.066 g/cm³, 9.07 times as dense as water. Its atoms have a radius of about 175 pm (Holmium next door is 175 pm). In the solid, its atoms pack into a hexagonal close-packed lattice.
Chemical behaviour
Its electronegativity is 1.24 on the Pauling scale. Pulling off its outermost electron takes 589 kJ/mol. A bond between erbium 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 Er³⁺. It shares much of its chemistry with the other lanthanides, especially its neighbours Dysprosium, Holmium, Thulium and Ytterbium.
Where it comes from
It makes up 3.5 mg/kg of Earth's crust, the 44th most abundant element there. It was first identified in 1843, making it the 57th element to be discovered (counting the 11 known since antiquity together).