Rhodium (Rh)
Element 45 · Transition metal · atomic mass 102.91 u · group 9, period 5
Electron shells: 2, 8, 18, 16, 1
Rhodium is one of the rarest and most expensive metals, and its job is almost entirely catalytic. It converts nitrogen oxides in car exhaust back to harmless nitrogen.
Rhodium has traded at many times the price of gold, driven almost entirely by emissions rules.
- Atomic number
- 45
- Atomic mass
- 102.91 u
- Electron configuration
- [Kr] 5s¹ 4d⁸
- Group · period · block
- 9 · 5 · d
- Oxidation states
- +3
- Electronegativity
- 2.28 (Pauling)
- Melting point
- 1,964 °C
- Boiling point
- 3,695 °C
- Density
- 12.4 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery-white, hard metal
- Discovered
- William Hyde Wollaston, 1803
45 protons, and 45 electrons when neutral
IUPAC standard atomic weight
Cobalt group
What Rhodium is used for
- Catalytic converters
- Reflective optical and jewellery plating
- Chemical catalysts
- Thermocouples
Atomic structure of Rhodium
A neutral rhodium atom has 45 protons and 45 electrons. Its most common isotope carries about 58 neutrons, which is where the mass number 103 comes from. Change the neutron count and you have a different isotope of rhodium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 16, 1. In orbital notation that is [Kr] 5s¹ 4d⁸. 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 Rhodium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Rhodium 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.
Discovery and naming
Rhodium was discovered by William Hyde Wollaston in 1803. Its name comes from Greek rhodon, "rose".
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 Rhodium?
The standard atomic weight of Rhodium is 102.91 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Rhodium have?
Rhodium has 45 protons, because the atomic number is the proton count and that is what makes an atom Rhodium at all. A neutral Rhodium atom has the same number of electrons, 45. The neutron count varies by isotope; the most common one has about 58, since 103 − 45 = 58.
What is the electron configuration of Rhodium?
The electron configuration of Rhodium is [Kr] 5s¹ 4d⁸. Its electrons are arranged 2, 8, 18, 16, 1 across 5 shells.
Is Rhodium a metal?
Yes. Rhodium is classified as a transition metal, on the metallic side of the table.
What group and period is Rhodium in?
Rhodium is in group 9 (the cobalt group), period 5, in the d-block. The group is its column and the period is its row.
What is the charge of Rhodium?
Rhodium most commonly forms a 3+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound.
What is the melting point of Rhodium?
Rhodium melts at 1,964 °C and boils at 3,695 °C. That puts it in the solids at everyday temperatures.
What is Rhodium used for?
Catalytic converters, Reflective optical and jewellery plating, Chemical catalysts, Thermocouples. Rhodium is one of the rarest and most expensive metals, and its job is almost entirely catalytic.
Who discovered Rhodium, and where does its name come from?
Rhodium (Rh) was discovered by William Hyde Wollaston in 1803. The name comes from Greek rhodon, "rose".