Roentgenium at a glance
- Atomic number
- 111
- Symbol
- Rg
- Atomic mass
- 282 u
- Category
- Transition metal
- Group / period
- 11 / 7
- Electron configuration
- [Rn] 5f 14 6d 9 7s 2
- State at 25 °C
- Unknown
- Melting point
- n/a
- Boiling point
- n/a
- Density
- 22 g/cm³
- Electronegativity
- n/a
- 1st ionization energy
- 1020 kJ/mol
- Oxidation states
- n/a
- Discovered
- 1994
Atomic structure
A neutral roentgenium atom has 111 protons and 111 electrons, and its most common isotope carries about 171 neutrons. One atom weighs about 4.68 × 10⁻²⁵ kg, so a mole of roentgenium (6.022 × 10²³ atoms) weighs 282 g. That nucleus holds 1.54 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 17, Q 2), which gives the configuration [Rn] 5f 14 6d 9 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 roentgenium has ever existed at once that its melting point, boiling point and even its state at room temperature are unknown. Its density is 22 g/cm³ (predicted), 22 times as dense as water, the 8th densest element.
Chemical behaviour
It has no measured electronegativity. Pulling off its outermost electron takes 1020 kJ/mol (predicted), more than Gold above it (890 kJ/mol). Group 11 also holds Copper, Silver and Gold, 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 bismuth-209 with nickel-64. Its longest-lived known isotope is Rg-282, about 100 seconds. It was first identified in 1994, making it the 111th element to be discovered (counting the 11 known since antiquity together).