Holmium at a glance
- Atomic number
- 67
- Symbol
- Ho
- Atomic mass
- 164.93 u
- Category
- Lanthanide
- Period
- 6
- Electron configuration
- [Xe] 4f 11 6s 2
- State at 25 °C
- Solid
- Melting point
- 1461 °C
- Boiling point
- 2720 °C
- Density
- 8.795 g/cm³
- Electronegativity
- 1.23
- 1st ionization energy
- 581 kJ/mol
- Oxidation states
- +3
- Discovered
- 1878
Atomic structure
A neutral holmium atom has 67 protons and 67 electrons, and its most common isotope carries about 98 neutrons. One atom weighs about 2.74 × 10⁻²⁵ kg, so a mole of holmium (6.022 × 10²³ atoms) weighs 164.93 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 29, O 8, P 2), which gives the configuration [Xe] 4f 11 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, Ho-165. No other element has a stable isotope with mass number 165, so Ho-165 has no stable isobars; its neighbours on that line decay into it or away from it.
Physical properties
At room temperature (25 °C) holmium is a solid. It melts at 1461 °C and boils at 2720 °C, so it stays liquid across a 1259-degree range. It stays solid in a candle flame (about 1000 °C) but would melt in molten iron (1538 °C). Its density is 8.795 g/cm³, 8.79 times as dense as water. Its atoms have a radius of about 175 pm (Dysprosium next door is 175 pm). In the solid, its atoms pack into a hexagonal close-packed lattice.
Chemical behaviour
Its electronegativity is 1.23 on the Pauling scale. Pulling off its outermost electron takes 581 kJ/mol. A bond between holmium 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 Ho³⁺. It shares much of its chemistry with the other lanthanides, especially its neighbours Terbium, Dysprosium, Erbium and Thulium.
Where it comes from
It makes up 1.3 mg/kg of Earth's crust, the 56th most abundant element there. It was first identified in 1878, making it the 65th element to be discovered (counting the 11 known since antiquity together).