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Rhodium

Element 45 · Transition metal

Specimen

Atomic number
45
Atomic mass
102.91
State at room temperature
Solid
Melting point
1,964 °C
Boiling point
3,695 °C
Density
12.4 g/cm³
Discovered
1803

Atomic mass from IUPAC.1 Other physical data from PubChem.2

Can I eat it?

In food and water
Not needed, little harm known. Rhodium has no known function in the body, and few safety data exist. For impurities in medicines, ICH uses the palladium limit of 100 micrograms a day by mouth. The RSC lists rhodium as a suspected cause of cancer. 34

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The atom

Rh
ShellElectrons
1 (K) 2
2 (L) 8
3 (M) 18
4 (N) 16
5 (O) outermost 1
Total45

Configuration [Kr] 4d⁸ 5s¹

4d ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↑
5s ↑
A shell diagram: each ring is an electron shell and each dot is one electron. The nucleus holds 45 protons. The outermost shell is shown in red. Electrons do not travel on rings: they fill orbitals, regions where an electron is likely to be found. The boxes are those orbitals for the electrons outside the Kr core, with one arrow per electron.

Related elements

Group 9
Co Cobalt Ir Iridium Mt Meitnerium

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Sources

  1. 1

    IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024. Abridged Standard Atomic Weights 2024 .

    The atomic mass shown for the 84 elements that have a standard atomic weight.

  2. 2

    National Center for Biotechnology Information (PubChem), 2026. Periodic Table of Elements .

    Electron configuration, melting and boiling points, density and discovery year for all 118 elements.

  3. 3

    International Council for Harmonisation (ICH), 2022. ICH Q3D(R2) Guideline for Elemental Impurities .

    Limits (permitted daily exposures) for metal impurities in medicines. Used here for the platinum-group metals, which no food authority covers.

    • There are very few published data on the safety of Iridium, Osmium, Rhodium and Ruthenium. ... Pd PDE will apply to iridium, osmium, rhodium, and ruthenium.
  4. 4

    Royal Society of Chemistry, 2026. Rhodium - Element information, properties and uses .

    • Rhodium has no known biological role. It is a suspected carcinogen.
  5. 5

    National Institute of Standards and Technology (NIST), 2026. Atomic Weights and Isotopic Compositions for All Elements .

    Isotopic composition of each element; the most abundant isotope sets the neutron count in the nucleus view.