Cadmium (Cd)

Cadmium poisoning produced itai-itai disease in Japan's Jinzū river basin from the 1910s, where mine runoff contaminated rice paddies and left people with bones so weakened that coughing broke ribs — the name means "it hurts, it hurts". The metal is a strong neutron absorber, and cadmium rods dropped into the Chicago Pile in 1942 were what held the first controlled chain reaction in check. Cadmium pigments give some of the most intense yellows and reds available to painters and are still used, under restriction, because nothing matches their opacity and permanence.

Properties

Atomic number

48

Symbol

Cd

Standard atomic weight

112.41 u

Category

Transition metal

Group

12

Period

5

Block

d-block

Electron configuration

[Kr] 5s² 4d¹⁰

Electrons per shell

2, 8, 18, 18, 2

Melting point

594.22 K — 321.1 °C — 609.9 °F

Boiling point

1,040 K — 766.9 °C — 1412.3 °F

Density

8.69 g/cm³

Electronegativity

1.69 (Pauling)

Oxidation states

+2

Discovered

1817 by Friedrich Stromeyer

Electron configuration

Full

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

Noble gas shorthand

[Kr] 5s² 4d¹⁰

Shells

K: 2 · L: 8 · M: 18 · N: 18 · O: 2

What it is used for

• Nickel-cadmium rechargeable cells, now largely superseded
• Cadmium telluride thin-film solar panels
• Cadmium yellow, orange and red artists' pigments
• Control rods and neutron shielding in reactors
• Quantum dots in some display backlights

Hazards

• Cumulative kidney and bone toxin with a biological half-life in the body of decades
• Classified as a human carcinogen by inhalation
• Cadmium fume from silver-soldering or brazing cadmium-bearing alloys can be fatal

Filed as a transition metal because it is in the d-block; under IUPAC's strict definition group 12 does not qualify, since the d subshell is full in every cadmium compound.

Neighbours in the table

Group 12

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Cadmium sits in group 12 with zinc, mercury, copernicium.