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An oxide (/ ˈ ɒ k s aɪ d /) is a chemical compound containing at least one oxygen atom and one other element [1] in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of –2) of oxygen, an O 2– ion with oxygen in the oxidation state of −2. Most of the Earth's crust consists of oxides. Even materials ...
2D diagram of mellitate C 12 O 6− 12, one of the oxocarbon anions. Black circles are carbon atoms, red circles are oxygen atoms. Each blue halo represents one half of a negative charge. In chemistry, an oxocarbon anion is a negative ion consisting solely of carbon and oxygen atoms, and therefore having the general formula C x O n−
The same structure occurs in so-called meta-vanadates, such as ammonium metavanadate, NH 4 VO 3. The formula of the oxyanion SiO 2− 3 is obtained as follows: each nominal silicon ion (Si 4+) is attached to two nominal oxide ions (O 2−) and has a half share in two others. Thus the stoichiometry and charge are given by:
The concentration of carbon dioxide (CO 2) in the atmosphere reached 427 ppm (0.04%) in 2024. [78] This is an increase of 50% since the start of the Industrial Revolution, up from 280 ppm during the 10,000 years prior to the mid-18th century. [79] [80] [81] The increase is due to human activity. [82]
Brodie also discovered in 1859 a fifth compound called graphite oxide, consisting of carbon and oxygen in ratios varying between 2:1 and 3:1; but the nature and molecular structure of this substance remained unknown until a few years ago, when it was renamed graphene oxide and became a topic of research in nanotechnology.
[5]: 108 In alkoxides, oxygen forms a single bond with carbon and accepts an electron from a metal to form an alkoxide anion, R–O −, with three lone pairs. In oxonium ions, one of oxygen's two lone pairs is used to form a third covalent bond which generates a cation, >O + – or =O + – or ≡O +, with one lone pair remaining.
The oxide crystal structure is based on a close-pack array of oxygen anions, with metal cations occupying interstitial sites. [1] The close-packed arrays, such as face-centered-cubic (fcc) and hexagonal-close packed (hcp), have both octahedral and tetrahedral interstices. [3]
In more acid conditions, aqueous carbon dioxide, CO 2 (aq), is the main form, which, with water, H 2 O, is in equilibrium with carbonic acid – the equilibrium lies strongly towards carbon dioxide. Thus sodium carbonate is basic, sodium bicarbonate is weakly basic, while carbon dioxide itself is a weak acid.