Lead dioxide

Lead(IV) oxide, commonly called lead dioxide or plumbic oxide or anhydrous plumbic acid is a chemical compound with the formula PbO₂. It is an oxide where lead is in an oxidation state +4. It is of an intermediate bond type, displaying both ionic (e.g. the lattice structure) and covalent (e.g. its low melting point and insolubility in water) properties. It is an odorless dark-brown crystalline powder which is nearly insoluble in water. It exists in two crystalline forms. The alpha phase has orthorhombic symmetry; it has been first synthesized in 1941 and identified in nature as a rare mineral scrutinyite in 1988. The more common, tetragonal beta phase was first identified as the mineral plattnerite around 1845 and later produced synthetically. Lead dioxide is a strong oxidizing agent which is used in the manufacture of matches, pyrotechnics, dyes and other chemicals. It also has several important applications in electrochemistry, in particular in the positive plates of lead acid batteries.

Lead(II) oxide

Lead(II) oxide, also called lead monoxide, is the inorganic compound with the molecular formula PbO. PbO occurs in two polymorphs, one litharge having a tetragonal crystal structure and the other massicot having an orthorhombic crystal structure. Modern applications for PbO are mostly in lead-based industrial glass and industrial ceramics, including computer components.

Preparation

PbO may be prepared by heating lead metal in air at approx. 600 °C. At this temperature it is also the end product of oxidation of other lead oxides in air:

Thermal decomposition of lead(II) nitrate or lead carbonate also results in the PbO formation:

PbO is produced on a large scale as an intermediate product in refining raw lead ores into metallic lead. The usual lead ore is galena (lead(II) sulfide). At high temperature (1000 °C) the sulfide is converted to the oxide:

Metallic lead is obtained by reducing the PbO with carbon monoxide at around 1200 °C:.

Structure

As determined by X-ray crystallography, both polymorphs, tetragonal and orthorhombic feature a pyramidal four-coordinate Pb center. In the tetragonal form the four Pb-O bonds have the same length, but in the orthorhombic two are shorter and two longer. The pyramidal nature indicates the presence of a stereo-chemically active lone pair of electrons. When PbO occurs in tetragonal lattice structure it is called litharge; and when the PbO has orthorhombic lattice structure it is called massicot. The PbO can be changed from massicot to litharge or vice versa by controlled heating and cooling. The tetragonal form is usually red or orange color, while the orthorhombic is usually yellow or orange, but the color is not a very reliable indicator of the structure. The tetragonal and orthorhombic forms of PbO occur naturally as rare minerals.

PBO

PBO may refer to: