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In the temperature ranges commonly used, the metal and the oxide are in a condensed state (solid or liquid), and oxygen is a gas with a much larger molar entropy. For the oxidation of each metal, the dominant contribution to the entropy change (ΔS) is the removal of 1 ⁄ 2 mol O 2, so that ΔS is negative and roughly equal for all metals.
The valence is the combining capacity of an atom of a given element, determined by the number of hydrogen atoms that it combines with. In methane, carbon has a valence of 4; in ammonia, nitrogen has a valence of 3; in water, oxygen has a valence of 2; and in hydrogen chloride, chlorine has a valence of 1.
Although most metal oxides are crystalline solids, many non-metal oxides are molecules. Examples of molecular oxides are carbon dioxide and carbon monoxide. All simple oxides of nitrogen are molecular, e.g., NO, N 2 O, NO 2 and N 2 O 4. Phosphorus pentoxide is a more complex molecular oxide with a deceptive name, the real formula being P 4 O 10.
Maghemite forms by weathering or low-temperature oxidation of spinels containing iron(II) such as magnetite or titanomagnetite. Maghemite can also form through dehydration and transformation of certain iron oxyhydroxide minerals, such as lepidocrocite and ferrihydrite .
Plutonium(IV) oxide, or plutonia, is a chemical compound with the formula Pu O 2. This high melting-point solid is a principal compound of plutonium . It can vary in color from yellow to olive green, depending on the particle size, temperature and method of production.
The bond-order formula at the bottom is closest to the reality of four equivalent oxygens each having a total bond order of 2. That total includes the bond of order 1 / 2 to the implied cation and follows the 8 − N rule [ 7 ] requiring that the main-group atom's bond-order total equals 8 − N valence electrons of the neutral atom ...
Lead(II) oxide, also called lead monoxide, is the inorganic compound with the molecular formula Pb O. PbO occurs in two polymorphs : litharge having a tetragonal crystal structure , and massicot having an orthorhombic crystal structure .
Cobalt(II,III) oxide is an inorganic compound with the formula Co 3 O 4. It is one of two well characterized cobalt oxides. It is a black antiferromagnetic solid.