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The oxidation state of oxygen is −2 in almost all known compounds of oxygen. The oxidation state −1 is found in a few compounds such as peroxides. Compounds containing oxygen in other oxidation states are very uncommon: − (superoxides), − (ozonides), 0 (elemental, hypofluorous acid), + (dioxygenyl), +1 (dioxygen difluoride), and +2 (oxygen difluoride). Oxygen is reactive and will form oxides with all other elements except the noble gases helium, neon, argon, and krypton.〔(Chemical properties of Oxygen ), Lenntech. Accessed January 25, 2008. "Oxygen is reactive and will form oxides with all other elements except helium, neon, argon and krypton."〕 ==Oxides== Water () is the oxide of hydrogen and most familiar oxygen compound. Its bulk properties partly result from the interaction of its component atoms, oxygen and hydrogen, with atoms of nearby water molecules. Hydrogen atoms are covalently bonded to oxygen in a water molecule but also have an additional attraction (about 23.3 kJ·mol−1 per hydrogen atom) to an adjacent oxygen atom in a separate molecule.〔P. Maksyutenko, T. R. Rizzo, and O. V. Boyarkin (2006). "A direct measurement of the dissociation energy of water", J. Chem. Phys. 125 doi 181101.〕 These hydrogen bonds between water molecules hold them approximately 15% closer than what would be expected in a simple liquid with just Van der Waals forces.〔Also, since oxygen has a higher electronegativity than hydrogen, the charge difference makes it a polar molecule. The interactions between the different dipoles of each molecule cause a net attraction force.〕 Due to its electronegativity, oxygen forms chemical bonds with almost all other free elements at elevated temperatures to give corresponding oxides. However, some elements, such as iron which oxidises to iron oxide, or rust, , readily oxidise at standard conditions for temperature and pressure (STP). The surface of metals like aluminium and titanium are oxidized in the presence of air and become coated with a thin film of oxide that passivates the metal and slows further corrosion.〔The aluminium oxide layer can be built to greater thickness by the process of electrolytic anodizing.〕 So-called noble metals, such as gold and platinum, resist direct chemical combination with oxygen, and substances like gold(III) oxide () must be formed by an indirect route. The alkali metals and alkali earth metals all react spontaneously with oxygen when exposed to dry air to form oxides, and form hydroxides in the presence of oxygen and water. As a result, none of these elements is found in nature as a free metal. Caesium is so reactive with oxygen that it is used as a getter in vacuum tubes. Although solid magnesium reacts slowly with oxygen at STP, it is capable of burning in air, generating very high temperatures, and its metal powder may form explosive mixtures with air. Oxygen is present as compounds in the atmosphere in trace quantities in the form of carbon dioxide () and oxides of nitrogen (NO''x''). The earth's crustal rock is composed in large part of oxides of silicon (silica , found in granite and sand), aluminium (aluminium oxide , in bauxite and corundum), iron (iron (III) oxide , in hematite and rust) and other oxides of metals. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Compounds of oxygen」の詳細全文を読む スポンサード リンク
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