Ruthenium (Ru)

Grubbs catalysts, ruthenium complexes that let chemists swap the ends of carbon-carbon double bonds under mild conditions, won the 2005 Nobel Prize in Chemistry and are now routine in pharmaceutical synthesis. Ruthenium is one of the rarest elements in the crust at about one part per billion, and nearly all of it comes as a by-product of platinum and nickel mining in South Africa and Russia. In 2017 a plume of ruthenium-106 drifted across Europe at levels far above background; it was traced by its isotope ratios to a reprocessing accident in the southern Urals that Russia has never acknowledged.

Properties

Atomic number

44

Symbol

Ru

Standard atomic weight

101.07 u

Category

Transition metal

Group

8

Period

5

Block

d-block

Electron configuration

[Kr] 5s¹ 4d⁷

Electrons per shell

2, 8, 18, 15, 1

Melting point

2,607 K — 2333.8 °C — 4232.9 °F

Boiling point

4,423 K — 4149.9 °C — 7501.7 °F

Density

12.1 g/cm³

Electronegativity

2.2 (Pauling)

Oxidation states

+3, +4, +8

Discovered

1844 by Karl Ernst Claus

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁷

Noble gas shorthand

[Kr] 5s¹ 4d⁷

Shells

K: 2 · L: 8 · M: 18 · N: 15 · O: 1

What it is used for

• Hardening platinum and palladium in electrical contacts and jewellery
• Thick-film resistors in almost all surface-mount electronics
• Ruthenium catalysts for ammonia synthesis and olefin metathesis
• Fountain pen nib tips, alloyed with iridium and osmium
• Dye-sensitised solar cell sensitisers

Anomalous electron configuration: [Kr] 5s¹ 4d⁷ rather than the predicted 5s² 4d⁶.

Neighbours in the table

Group 8

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Ruthenium sits in group 8 with iron, osmium, hassium.