Nickel carbonyl is the organonickel compound

Organonickel

Organonickel chemistry is a branch of organometallic chemistry that deals with organic compounds feature nickel-carbon bonds. They are used as a catalyst, as a building block in organic chemistry and in chemical vapor deposition. Organonickel compounds are also short-lived intermediates in organic...

 with the formula

Chemical formula

A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 Ni(CO)₄. This pale-yellow liquid is the principal carbonyl

Metal carbonyl

Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. These complexes may be homoleptic, that is containing only CO ligands, such as nickel carbonyl , but more commonly metal carbonyls contain a mix of ligands, such as Re3Cl...

 of nickel. It is an intermediate in the Mond process

Mond process

The Mond process, sometimes known as the carbonyl process is a technique created by Ludwig Mond in 1890 to extract and purify nickel. The process was used commercially before the end of the 19th century...

 for the purification of nickel

Nickel

Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

 and a reagent in organometallic chemistry

Organometallic chemistry

Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...

. Nickel carbonyl is the most toxic substance encountered in industrial processes.
Nickel tetracarbonyl contains nickel in the zero oxidation state. It has 18 valence electron

Valence electron

In chemistry, valence electrons are the electrons of an atom that can participate in the formation of chemical bonds with other atoms. Valence electrons are the "own" electrons, present in the free neutral atom, that combine with valence electrons of other atoms to form chemical bonds. In a single...

, and is a tetrahedral molecule with four carbonyl

Carbonyl

In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups....

 (carbon monoxide

Carbon monoxide

Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

) ligands attached to nickel.