#45 / 118
45Rh102.91
Transition Metalssolid at STPD-block

Rhodium

Group: 9Period: 5Standard Atomic Weight: 102.91 u

Why is Rhodium in this position?

Understanding the scientific rationale behind Rhodium's position in the periodic table:

Group Assignment
Group 9

Belongs to Group 9 because it has 9 valence electrons (4d⁸ 5s¹).

Period Assignment
Period 5

Belongs to Period 5 because its outermost electron occupies n=5.

Orbital Block
D-block

Belongs to the d-block because its differentiating electrons occupy the 4d subshell.

Chemical Category
Transition Metals

Classified as a transition metal and noble platinum group metal with high catalytic activity.

Atomic Structure & Bohr Shell Model

Shell Distribution: [2, 8, 18, 16, 1]

Bohr Atomic Shell Model(2, 8, 18, 16, 1)

Hover or tap any shell orbit ring to inspect electron counts and 2n² capacities.

45 Protons (p⁺)58 Neutrons (n⁰)
KShell K: Electron 1 of 2Shell K: Electron 2 of 2LShell L: Electron 1 of 8Shell L: Electron 2 of 8Shell L: Electron 3 of 8Shell L: Electron 4 of 8Shell L: Electron 5 of 8Shell L: Electron 6 of 8Shell L: Electron 7 of 8Shell L: Electron 8 of 8MShell M: Electron 1 of 18Shell M: Electron 2 of 18Shell M: Electron 3 of 18Shell M: Electron 4 of 18Shell M: Electron 5 of 18Shell M: Electron 6 of 18Shell M: Electron 7 of 18Shell M: Electron 8 of 18Shell M: Electron 9 of 18Shell M: Electron 10 of 18Shell M: Electron 11 of 18Shell M: Electron 12 of 18Shell M: Electron 13 of 18Shell M: Electron 14 of 18Shell M: Electron 15 of 18Shell M: Electron 16 of 18Shell M: Electron 17 of 18Shell M: Electron 18 of 18NShell N: Electron 1 of 16Shell N: Electron 2 of 16Shell N: Electron 3 of 16Shell N: Electron 4 of 16Shell N: Electron 5 of 16Shell N: Electron 6 of 16Shell N: Electron 7 of 16Shell N: Electron 8 of 16Shell N: Electron 9 of 16Shell N: Electron 10 of 16Shell N: Electron 11 of 16Shell N: Electron 12 of 16Shell N: Electron 13 of 16Shell N: Electron 14 of 16Shell N: Electron 15 of 16Shell N: Electron 16 of 16OShell O: Electron 1 of 1RhZ = 45

Educational Note: This Niels Bohr planetary model visually illustrates principal quantum energy shells ($n=1, 2, 3\dots$) and electron counts. In modern quantum mechanics (Schrödinger model), electrons do not orbit in fixed circular planetary tracks, but exist as 3D probability clouds (orbitals: $s, p, d, f$) governed by the Heisenberg uncertainty principle.

Electron Shell Filling Breakdown

Shell K (n=1):2 / 2 electrons (100%)
Shell L (n=2):8 / 8 electrons (100%)
Shell M (n=3):18 / 18 electrons (100%)
Shell N (n=4):16 / 32 electrons (50%)
Shell O (n=5):1 / 50 electrons (2%)
Aufbau Electron Configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁸ 5s¹

Neutral ground state configuration. Valence electrons: 9.

Atomic & Quantum Properties

Electronegativity (Pauling)2.28 Pauling
1st Ionization Energy719.7 kJ/mol
Electron Affinity-109.7 kJ/mol
Atomic Radius (empirical)173 pm
Common Oxidation States+3
Crystal StructureFCC

Physical & Thermal Properties

Density at STP12.41 g/cm³
Melting Point1964 °C (2237 K)
Boiling Point3695 °C (3968 K)
Magnetic OrderingParamagnetic
Discovery Year1804
Discovered ByWilliam Hyde Wollaston

Real-World Uses, Occurrence & Compounds

Major Industrial & Everyday Uses
  • Three-way automotive catalytic converters reducing toxic nitrogen oxides (NOx) into harmless N₂
  • Rhodium electroplating giving white gold and sterling silver brilliant shine and tarnish protection
  • High-temperature laboratory crucibles and aircraft spark plug electrodes
  • Industrial chemical synthesis catalysts (Wilkinson's catalyst for alkene hydrogenation)
Occurrence in Nature

Exceptionally scarce in Earth's crust; mined almost exclusively in the Bushveld Igneous Complex in South Africa as a platinum coproduct.

Etymology & Name Origin

From Greek 'rhodon' meaning rose, due to the deep rose-red color of its chlorine salts

Important Chemical Compounds
RhCl₃ (Rhodium trichloride)
Rh₂O₃ (Rhodium oxide)
Wilkinson's catalyst [RhCl(PPh₃)₃]
Interesting Chemical Facts
  • Over 80% of global rhodium production is consumed by automotive catalytic converters to purge exhaust gases of smog-causing nitrogen oxides.
  • In 2021, rhodium reached an all-time price record of over $29,000 per troy ounce—more than 15 times the price of gold.
  • Sir William Wollaston discovered rhodium in crude South American platinum ore shortly after discovering palladium.
Safety & Handling Note

Bulk metallic rhodium is completely non-toxic and hypoallergenic; rhodium chloride complexes are skin and respiratory irritants.