Nihonium at a glance
- Atomic number
- 113
- Symbol
- Nh
- Atomic mass
- 286 u
- Category
- Post-transition metal
- Group / period
- 13 / 7
- Electron configuration
- [Rn] 5f 14 6d 10 7s 2 7p 1
- State at 25 °C
- Unknown
- Melting point
- n/a
- Boiling point
- n/a
- Density
- 16 g/cm³
- Electronegativity
- n/a
- 1st ionization energy
- 707 kJ/mol
- Oxidation states
- n/a
- Discovered
- 2004
Atomic structure
A neutral nihonium atom has 113 protons and 113 electrons, and its most common isotope carries about 173 neutrons. One atom weighs about 4.75 × 10⁻²⁵ kg, so a mole of nihonium (6.022 × 10²³ atoms) weighs 286 g. That nucleus holds 1.53 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 18, Q 3), which gives the configuration [Rn] 5f 14 6d 10 7s 2 7p 1. With 3 electrons in its outer shell, it tends to lose electrons and form positive ions. Every isotope is radioactive and short-lived; only a handful of atoms have ever been made, one at a time.
Physical properties
So little nihonium has ever existed at once that its melting point, boiling point and even its state at room temperature are unknown. Its density is 16 g/cm³ (predicted), 16 times as dense as water.
Chemical behaviour
It has no measured electronegativity. Pulling off its outermost electron takes 707 kJ/mol (predicted), more than Thallium above it (589 kJ/mol). Group 13 also holds Boron, Aluminium, Gallium, Indium and Thallium, which share its outer-shell pattern. Its Lewis symbol is Nh surrounded by 3 dots. 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 RIKEN in Japan, after nine years of experiments that produced only three atoms by fusing bismuth-209 with zinc-70. Its longest-lived known isotope is Nh-286, about 10 seconds. It was first identified in 2004, making it the 117th element to be discovered (counting the 11 known since antiquity together).