Roentgenium (Rg)
Element 111 · Transition metal · atomic mass [282] u · group 11, period 7
Electron shells: 2, 8, 18, 32, 32, 17, 2
Roentgenium sits below gold and is predicted to be chemically similar, though nobody has enough to check properly. It was confirmed on the centenary of the X-ray's discovery.
Element 111 was named for Röntgen exactly 100 years after he discovered X-rays.
- Atomic number
- 111
- Atomic mass
- [282] u
- Electron configuration
- [Rn] 7s² 5f¹⁴ 6d⁹
- Group · period · block
- 11 · 7 · d
- Oxidation states
- −1, +1, +3, +5
- Electronegativity
- Not measured
- Melting point
- —
- Boiling point
- —
- Density
- Not measured
- State at 20 °C
- Unknown
- Appearance
- Unknown; presumed metallic
- Discovered
- Sigurd Hofmann and colleagues, 1994
111 protons, and 111 electrons when neutral
Mass number of the longest-lived isotope — no standard atomic weight exists
Predicted, not measured
Coinage metals
What Roentgenium is used for
- Scientific research only
Atomic structure of Roentgenium
A neutral roentgenium atom has 111 protons and 111 electrons. Its most common isotope carries about 171 neutrons, which is where the mass number 282 comes from. Change the neutron count and you have a different isotope of roentgenium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 32, 17, 2. In orbital notation that is [Rn] 7s² 5f¹⁴ 6d⁹. As a d-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Roentgenium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Roentgenium sits in the periodic table
The d-block. Multiple stable oxidation states give them coloured compounds, catalytic ability and the strength that makes them the working metals of industry.
- Directly above: Gold — same group, so similar chemistry with a smaller atom.
- One proton lighter: Darmstadtium.
- One proton heavier: Copernicium.
Discovery and naming
Roentgenium was discovered by Sigurd Hofmann and colleagues in 1994. Its name comes from Wilhelm Conrad Röntgen, discoverer of X-rays, which is also why its symbol (Rg) does not match its English name.
Every isotope of roentgenium is radioactive, so it has no standard atomic weight. Periodic tables show the mass number of its longest-lived isotope in square brackets instead.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Roentgenium?
Roentgenium has no stable isotope, so it has no standard atomic weight. Periodic tables instead show 282 in square brackets — the mass number of its longest-lived isotope.
How many protons, neutrons and electrons does Roentgenium have?
Roentgenium has 111 protons, because the atomic number is the proton count and that is what makes an atom Roentgenium at all. A neutral Roentgenium atom has the same number of electrons, 111. The neutron count varies by isotope; the most common one has about 171, since 282 − 111 = 171.
What is the electron configuration of Roentgenium?
The electron configuration of Roentgenium is [Rn] 7s² 5f¹⁴ 6d⁹, though for an element this heavy the configuration is predicted from theory rather than measured. Its electrons are arranged 2, 8, 18, 32, 32, 17, 2 across 7 shells.
Is Roentgenium a metal?
Yes. Roentgenium is classified as a transition metal, on the metallic side of the table.
What group and period is Roentgenium in?
Roentgenium is in group 11 (the coinage metals), period 7, in the d-block. The group is its column and the period is its row.
What is Roentgenium used for?
Scientific research only. Roentgenium sits below gold and is predicted to be chemically similar, though nobody has enough to check properly.
Who discovered Roentgenium, and where does its name come from?
Roentgenium (Rg) was discovered by Sigurd Hofmann and colleagues in 1994. The name comes from Wilhelm Conrad Röntgen, discoverer of X-rays.
Is Roentgenium radioactive?
Yes. Every isotope of Roentgenium is radioactive — it has no stable form at all, which is why the periodic table shows its mass in square brackets rather than as a standard atomic weight.