Cadmium (Cd)
“The soft, silvery metal behind classic rechargeable batteries — and behind one of history’s most painful poisoning episodes.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
The notes
Characteristics
- A d-block metal with configuration [Kr] 4d¹⁰ 5s²: it sheds its two outer electrons to form Cd²⁺ and sits in Period 5, Group 12 beside zinc and mercury.
- Dangerously toxic even at low, long-term exposure: cadmium lodges in the kidneys for decades, and mine-waste water in Japan once poisoned rice paddies, causing the agonising “itai-itai” bone disease.
- Resists corrosion and alkalis remarkably well, so thin electroplated cadmium coats once protected bolts and aircraft landing-gear parts from salt spray.
- The isotope cadmium-113 devours neutrons, which lets cadmium control rods tame a nuclear chain reaction inside a reactor core.
A soft, silvery-white metal with a faint blue tinge, easily cut with a knife. Freshly cut faces shine brightly before slowly dulling in moist air, and a cadmium bar feels distinctly heavier than a same-sized bar of zinc.
Where you meet it
✦ Uses
- Nickel-cadmium (Ni-Cd) rechargeable batteries — the rugged cells that long powered emergency lights, cordless phones and power tools in Bangladeshi homes.
- Cadmium sulfide and selenide pigments — the brilliant cadmium yellow and cadmium red of artists’ oil paints and older bright plastics.
- Electroplated cadmium coatings that sacrifice themselves to shield steel bolts and aircraft parts from rusting in salty air.
- Neutron-hungry control rods for nuclear reactors; cadmium selenide quantum dots still light up premium QLED television screens.
◍ Everyday examples
- The elderly Ni-Cd battery pack inside a household emergency lamp or an old cordless phone.
- Cigarette smoke carries cadmium deep into the lungs — smokers typically carry roughly twice the cadmium burden of non-smokers.
- Rice grown on cadmium-contaminated soil can pass the metal into its grains — one reason food regulators watch heavy-metal levels so strictly.
History & name
In 1817 the German chemist Friedrich Stromeyer, inspecting pharmacy stocks, noticed that some samples of calamine (zinc carbonate) turned dirty yellow on heating while others stayed white. Chasing the difference, he reduced the ore with carbon and obtained a new soft, blue-white metal, which he named cadmium after the Latin cadmia — the ancient name for calamine ore. That same year Karl Samuel Leberecht Hermann independently identified the metal, making cadmium one of the very first elements discovered hiding inside a mineral impurity.