GROUP 9: COBALT GROUP

Cobalt Group Overview

Also known as: Cobalt family

Group Members: Cobalt (Co), Rhodium (Rh), Iridium (Ir), Meitnerium (Mt)

Common Properties: All are transition metals, form +3 oxidation state, magnetic properties, catalytic activity

Co

Cobalt

Magnetic
Atomic Number 27
Atomic Mass 58.93 u
Electron Config [Ar] 3d⁷ 4s²
Common Ions Co²⁺, Co³⁺
Melting Point 1495°C
Density 8.90 g/cm³
Cobalt gives glass and ceramics a beautiful deep blue color!

Properties: Hard, lustrous, silver-gray, ferromagnetic

Applications: Superalloys, magnets, batteries, pigments, radiotherapy

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Rh

Rhodium

Precious
Atomic Number 45
Atomic Mass 102.91 u
Electron Config [Kr] 4d⁸ 5s¹
Common Ions Rh³⁺
Melting Point 1964°C
Density 12.41 g/cm³
Rhodium is the most expensive precious metal - more valuable than gold or platinum!

Properties: Hard, silvery-white, corrosion-resistant, reflective

Applications: Catalytic converters, jewelry plating, electrical contacts, mirrors

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Ir

Iridium

Dense
Atomic Number 77
Atomic Mass 192.22 u
Electron Config [Xe] 4f¹⁴ 5d⁷ 6s²
Common Ions Ir³⁺, Ir⁴⁺
Melting Point 2466°C
Density 22.56 g/cm³
Iridium is found in meteorites and is associated with the asteroid that killed the dinosaurs!

Properties: Very dense, corrosion-resistant, hard, brittle

Applications: Spark plugs, crucibles, compass bearings, standard meter bar

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Mt

Meitnerium

Synthetic
Atomic Number 109
Atomic Mass 278 u
Electron Config [Rn] 5f¹⁴ 6d⁷ 7s²
Common Ions Mt³⁺
Half-life ~8 seconds
Stability Synthetic
Meitnerium is named after Lise Meitner, the physicist who discovered nuclear fission!

Properties: Synthetic radioactive metal, extremely short-lived

Applications: Scientific research only

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