An oxide is a chemical compound containing an oxygen atom and other elements. Most of the earth's crust consists of oxides. Oxides result when elements are oxidized by air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon monoxide and carbon dioxide. Even materials that are considered to be pure elements often contain a coating of oxides. For example, aluminium foil has a thin skin of Al2O3 that protects the foil from further corrosion.
PbO is prepared by heating lead metal in air at 600 C. Alternatively, it is obtained by the thermal decomposition of lead(II) nitrate or lead carbonate:
2Pb(NO3)2) 2PbO + 4NO2 + O2
PbCO3 PbO + CO2
The structure of the solid, determined by X-ray crystallography, reveals a pyramidal four-coordinate Pb center. The pyramidal nature indicates the presence of a stereochemically active lone pair of electrons
The red and yellow forms of this material are related by a small change in enthalpy: PbO(red) PbO(yellow) ?H = 1.6 kJ/mol
PbO is amphoteric, which means that it reacts with both acids and with bases. With acids, it forms salts of Pb2+ via the intermediacy of oxo clusters such as [Pb6O(OH)6]4+. With strong base, PbO dissolves to form plumbite(II) salts: PbO + H2O + OH- [Pb(OH)3]-
Zinc oxide is a chemical compound with the formula ZnO. It is nearly insoluble in water but soluble in acids and alkalis. It occurs as white hexagonal crystals or a white powder commonly known as zinc white. It remains white when exposed to hydrogen sulfide or ultraviolet light. Crystalline zinc oxide exhibits the piezoelectric effect and is thermochromic (it will change colour from white to yellow when heated, and back again when cooled down). Zinc oxide decomposes into zinc vapor and oxygen at around 1975 °C. High-quality single-crystalline ZnO is almost transparent. Zinc oxide occurs in nature as the mineral zincite.