Cadmium

Cadmium is a metal. It is element 48 on the periodic table. Its symbol is Cd. Its atomic number is 48 and its atomic mass is 112.4. It is found in Group 12 on the periodic table.

Cadmium,  ₄₈Cd

General properties
Pronunciation	/ˈkædmiəm/ ​(KAD-mee-əm)
Appearance	silvery bluish-gray metallic
Standard atomic weight (Ar, standard)	112.414(4)
Cadmium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Zn ↑ Cd ↓ Hg silver ← cadmium → indium
Atomic number (Z)	48
Group	group 12
Period	period 5
Block	d-block
Element category	post-transition metal, alternatively considered a transition metal
Electron configuration	[Kr] 4d10 5s2
Electrons per shell	2, 8, 18, 18, 2
Physical properties
Phase at STP	Cd: Solid
Melting point	594.22 K ​(321.07 °C, ​609.93 °F)
Boiling point	1040 K ​(767 °C, ​1413 °F)
Density (near r.t.)	8.65 g/cm3
when liquid (at m.p.)	7.996 g/cm3
Heat of fusion	6.21 kJ/mol
Heat of vaporization	99.87 kJ/mol
Molar heat capacity	26.020 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 530 583 654 745 867 1040
Atomic properties
Oxidation states	−2, +1, +2 (a mildly basic oxide)
Electronegativity	Pauling scale: 1.69
Ionization energies	1st: 867.8 kJ/mol 2nd: 1631.4 kJ/mol 3rd: 3616 kJ/mol
Atomic radius	empirical: 151 pm
Covalent radius	144±9 pm
Van der Waals radius	158 pm
Spectral lines of cadmium
Other properties
Natural occurrence	Cd: Primordial
Crystal structure	​hexagonal close-packed (hcp)
Speed of sound thin rod	2310 m/s (at 20 °C)
Thermal expansion	30.8 µm/(m·K) (at 25 °C)
Thermal conductivity	96.6 W/(m·K)
Electrical resistivity	72.7 nΩ·m (at 22 °C)
Magnetic ordering	diamagnetic
Magnetic susceptibility	−19.8·10−6 cm3/mol
Young's modulus	50 GPa
Shear modulus	19 GPa
Bulk modulus	42 GPa
Poisson ratio	0.30
Mohs hardness	2.0
Brinell hardness	203–220 MPa
CAS Number	7440-43-9
History
Discovery and first isolation	Karl Samuel Leberecht Hermann and Friedrich Stromeyer (1817)
Named by	Friedrich Stromeyer (1817)
Main isotopes of cadmium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct 106Cd 1.25% stable 107Cd syn 6.5 h ε 107Ag 108Cd 0.89% stable 109Cd syn 462.6 d ε 109Ag 110Cd 12.47% stable 111Cd 12.80% stable 112Cd 24.11% stable 113Cd 12.23% 7.7×1015 y β− 113In 113mCd syn 14.1 y β− 113In IT 113Cd 114Cd 28.75% stable 115Cd syn 53.46 h β− 115In 116Cd 7.51% 3.1×1019 y β−β− 116Sn

Properties

Physical properties

Cadmium is a blue-gray soft metal. It can be considered a transition metal or a post-transition metal. It is malleable and ductile. It is similar to zinc. It melts at 321°C.

Cadmium has 8 natural isotopes. 5 are radioactive, but 3 have very long half-lives so their radioactivity is almost nothing.

Chemical properties

Cadmium is a moderately reactive metal. It corrodes in moist air and dissolves in acids. It burns in air when powdered to make the brown cadmium oxide.

Chemical compounds

Cadmium chloride

Cadmium oxide

Cadmium forms chemical compounds in two oxidation states: +1 and +2. The +1 state is rare and unstable. The +2 state is much more common. Most +2 compounds dissolve easily in water and are white to yellow. Cadmium oxide can be brown, red, or white. Cadmium sulfide is bright yellow. Cadmium chloride and cadmium sulfate are colorless solids that dissolve easily in water. Cadmium fluoride is slightly soluble. Cadmium compounds are toxic when inhaled.

• Cadmium bromide, pale yellow solid, dissolves in water
• Cadmium chloride, colorless solid, dissolves in water
• Cadmium fluoride, gray solid, does not dissolve good in water
• Cadmium iodide, pale yellow solid, dissolves in water
• Cadmium oxide, white, brown, or red solid, dissolves in acids
• Cadmium sulfate, colorless solid, dissolves in water
• Cadmium sulfide, bright yellow solid, does not dissolve in water
• Cadmium telluride, black solid, semiconductor

History

Cadmium was found by two chemists, German chemist Friedrich Stromeyer discovered it in 1817, and Karl Herman also discovered it in 1818. They were looking at an impurity in zinc carbonate and found cadmium. For about 100 years, Germany made most cadmium. Cadmium iodide was used as a medicine although it was toxic.

Occurrence

Greenockite (yellow crystal)

Cadmium ores are rare. Greenockite, a cadmium sulfide mineral is the only main ore and it is found with sphalerite, a zinc sulfide. Because of this, most cadmium comes from zinc processing. Cadmium as a metal is very rare but is found in one place in Russia.

Preparation

China makes the most cadmium. South Korea and Japan also make cadmium. Cadmium is taken from the zinc metal by heating the zinc metal in a vacuum. Cadmium is boiled first. The cadmium is condensed and used. Cadmium is also taken by precipitating it from the solution of zinc sulfate used to make pure zinc by electrolysis.

Uses

In the 1930s and 1940s cadmium was mainly used to plate steel to prevent it from corroding. Then cadmium sulfide was used as a pigment in paint.

Now, cadmium is mainly used in nickel cadmium batteries. 86% of cadmium is used in batteries as of 2009. Some people are trying to stop using nickel-cadmium batteries because cadmium is toxic. Cadmium is still used to electroplate steel to prevent corrosion. Only about 6% of cadmium is used for this. Cadmium is also used in lasers, nuclear reactors, phosphors, photoresistors, pigments, and semiconductors. Wood's metal, an alloy that melts very easily, has cadmium in it. Cadmium is used in some solder.

Cadmium is not used in the human body or any other animal. A diatom uses cadmium, though.

Safety

Cadmium is a highly toxic metal. Dust of cadmium or its compounds is very dangerous and can kill. Some countries have banned cadmium from electronics. Cigarette smoking is the most important source of cadmium. Smokers have about 4 times more cadmium in their blood than nonsmokers (people who do not smoke). Cadmium is thought to be carcinogenic, although people still debate whether it is other things with the cadmium that cause cancer, like arsenic.