Hassium at a glance
- Atomic number
- 108
- Symbol
- Hs
- Atomic mass
- 277 u
- Category
- Transition metal
- Group / period
- 8 / 7
- Electron configuration
- [Rn] 5f 14 6d 6 7s 2
- State at 25 °C
- Unknown
- Melting point
- n/a
- Boiling point
- n/a
- Density
- 28.6 g/cm³
- Electronegativity
- n/a
- 1st ionization energy
- 730 kJ/mol
- Oxidation states
- +8 (pred.)
- Discovered
- 1984
Atomic structure
A neutral hassium atom has 108 protons and 108 electrons, and its most common isotope carries about 169 neutrons. One atom weighs about 4.6 × 10⁻²⁵ kg, so a mole of hassium (6.022 × 10²³ atoms) weighs 277 g. That nucleus holds 1.56 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 14, Q 2), which gives the configuration [Rn] 5f 14 6d 6 7s 2. As a d-block element, both its outer s electrons and its inner d electrons can take part in bonding, which is why it shows more than one oxidation state. Every isotope is radioactive and short-lived; only a handful of atoms have ever been made, one at a time.
Physical properties
So little hassium has ever existed at once that its melting point, boiling point and even its state at room temperature are unknown. Its density is 28.6 g/cm³ (predicted), 28.6 times as dense as water, the 1st densest element.
Chemical behaviour
It has no measured electronegativity. Pulling off its outermost electron takes 730 kJ/mol (predicted), less than Osmium above it (840 kJ/mol). Group 8 also holds Iron, Ruthenium and Osmium, which share its outer-shell pattern. 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 GSI Darmstadt by fusing lead-208 with iron-58. Its longest-lived known isotope is Hs-269, around 10 seconds. It was first identified in 1984, making it the 109th element to be discovered (counting the 11 known since antiquity together).