Atomic number 48

Cadmium

Cd
+ phase
− phase

Shells Orbitals 4d 5s

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48 electrons in 5 shells: 2, 8, 18, 18, 2.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Transition metal
Period: 5
Group: 12
Block: d
Standard atomic weight: 112.41(1) Da
Electron configuration: [Kr] 4d¹⁰ 5s²
Phase at 25 °C: solid
Melting point: 321.07 °C
Boiling point: 767 °C
Density: 8.69 g/cm³
Electronegativity (Pauling): 1.69
Discovered: 1817, Friedrich Stromeyer

Neighbours in the table

Ag In

Cadmium gave itself away by changing colour. In 1817 Friedrich Stromeyer heated samples of calamine, a zinc carbonate ore, and saw that some glowed yellow while others stayed as they were. Those that changed colour held traces of a new element. Jefferson Lab, in PubChem’s element record, calls Stromeyer a chemist. CIAAW’s note in the same record makes him a German physician.

The configuration is [Kr] 4d¹⁰ 5s². IUPAC excludes filled-d elements from the transition elements, OpenStax notes. Its chapter on periodicity files group 12 with the post-transition metals, noting that its final electron enters an s orbital, not a d. Without the 5s pair, Cd²⁺ is [Kr] 4d¹⁰, which OpenStax calls a pseudo-noble gas configuration. Jefferson Lab gives its oxidation state, a hypothetical all-ionic charge, as +2; Los Alamos adds +1 and −2.

Los Alamos describes a soft, bluish-white metal that a knife cuts easily. OpenStax finds the chemistry of cadmium and zinc much alike: both sit below hydrogen in reduction potential and give off hydrogen gas with acids. Moist air slowly turns the surface to cadmium oxide, PubChem’s safety record notes.

Where it is found

PubChem’s element record gives 0.15 milligrams of cadmium per kilogram of crust and 1.1 × 10⁻⁴ milligrams per litre of seawater. Greenockite, CdS, is the one mineral with much of it, and Jefferson Lab says it is too scarce to mine at a profit. Cadmium shares chemical properties with zinc and often takes zinc’s place in the crystal lattice of sphalerite, ZnS. The US Geological Survey puts the cadmium content of typical zinc ores at about 0.03 per cent.

Cadmium is therefore mainly a by-product of zinc refining; Los Alamos adds copper and lead ores as sources. In the smelting route OpenStax describes, crude zinc comes off with cadmium in it; cadmium boils at 767 °C, lower than zinc, so it is distilled off. The only American zinc smelter takes another path, leaching roasted sulfide concentrates, and recovered an estimated 300 tons of cadmium in 2024. The survey puts world refinery output that year at 24,000 metric tons, with China at 9,300 and the Republic of Korea at 4,500. Spent NiCd batteries supply most of the recycled metal.

Why it matters

Nickel-cadmium (NiCd) batteries take most cadmium, the survey says, ahead of alloys, coatings and pigments. In OpenStax’s description of the cell, a cadmium-plated anode and a nickel-plated cathode sit in potassium hydroxide. On discharge cadmium metal becomes cadmium hydroxide, Cd(OH)₂, while nickel(IV) oxide is reduced, giving about 1.2 V. The cell recharges about 1000 times, and its jelly-roll layout delivers far more current than an alkaline cell of similar size.

The newer demand is in semiconductors. Cadmium telluride, CdTe, goes into thin-film solar panels, and cadmium zinc telluride, CdZnTe, is a substrate for radiation detectors and imaging. One Ohio-based maker opened a fourth plant, in Alabama, in 2024. That brought its capacity to almost 11 gigawatts of CdTe panels a year, against world capacity of about 21 GW, by the survey’s count. Lithium-ion cells, the survey adds, can replace NiCd in many applications.

Electroplating is among its uses, Los Alamos says, while the 2025 survey names batteries first. Cadmium absorbs neutrons easily, Jefferson Lab notes, which is why reactor control rods use it; OpenStax lists boron and hafnium as other absorbers.

Properties

Properties of cadmium Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	48
Standard atomic weight	112.41(1) Da	Da	IUPAC/CIAAW 2024
Melting point	321.07 °C	°C	Los Alamos: 321.07 °C
Boiling point	767 °C	°C	Los Alamos: 767 °C
Density	8.69 g/cm³	g/cm³
Electronegativity (Pauling)	1.69
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰
Phase at 25 °C	solid

Safety

Cadmium metal is toxic, above all as dust or fume breathed in. PubChem’s record carries the signal word Danger with the statements fatal if inhaled, may cause cancer, and organ damage from prolonged or repeated exposure. NIOSH treats it as a potential occupational carcinogen and names the respiratory system, kidneys, prostate and blood as target organs. PubChem’s safety record adds that neither smell nor irritation warns of over-exposure, and its Laboratory Chemical Safety Summary and the NIOSH card below set out the workplace precautions.

Questions

Is cadmium dangerous to humans?

Yes, both at once and over years: PubChem's hazard classification rates the metal fatal if inhaled. The EPA, in a summary of cadmium compounds, says long-term breathing or swallowing of cadmium lets it collect in the kidneys, where it can cause kidney disease. The International Chemical Safety Card quoted by PubChem calls the metal carcinogenic to humans, while the EPA ranks cadmium a probable human carcinogen. Breathing hot fume can also bring on metal fume fever, with delayed effects.

What is cadmium used for besides batteries?

Los Alamos lists bearing alloys with low friction and great resistance to fatigue, several solders, and some of the lowest-melting alloys known. Jefferson Lab, in PubChem's element record, adds that hydrated cadmium sulfate is used in the Weston cell, which gives a precise voltage for calibrating medical and laboratory equipment. IUPAC notes that the isotope cadmium-112 is used to make indium-111, a diagnostic radioisotope whose half-life is 2.8047 days in the evaluation of the International Atomic Energy Agency (IAEA).

Where does the name cadmium come from?

From the ore it was found in. Los Alamos traces the word to the Latin cadmia and the Greek kadmeia, the ancient names for calamine, a zinc carbonate. CIAAW's note in PubChem's element record connects that ore name to Cadmus, the mythical king of Phoenicia who founded Thebes. The same note says the ore may have turned up in furnace flue dust at Thebes.

How many stable isotopes does cadmium have?

Natural cadmium is a mix of eight isotopes, cadmium-114 the commonest at about 28.8 per cent. Jefferson Lab counts three as stable. The Atomic Mass Data Center (AMDC) and IAEA data in PubChem's record list six, three of them with only a lower limit on the half-life, and give cadmium-113 a half-life of 8.04 × 10¹⁵ years by beta decay and cadmium-116 one of 26.9 × 10¹⁸ years by double beta decay.