Lead(II) oxide

Lead(II) oxide is the chemical compound with the formula PbO. Lead(II) oxide occurs in two forms: red, having a tetragonal crystal structure and yellow, having an orthorhombic crystal structure. Both forms occur naturally as minerals: the red form is known as litharge and the yellow form is known as massicot.

Preparation and structure
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.

Reactions
The red and yellow forms of this material are related by a small change in enthalpy: PbO(red) →  PbO(yellow)  ΔH = 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]-

Applications
PbO is a component of lead paints and is used extensively in manufacturing of lead glasses and ceramic glazes. PbO is the main ingredient of the paste used for filling the plates during manufacturing of lead-acid batteries. A mixture of PbO with glycerine sets to a hard, waterproof cement that has been used to join the flat glass sides and bottoms of aquaria, and was also once used to seal glass panels in window frames.

PbO is used in vulcanization of rubber. PbO is used in certain condensation reactions in organic synthesis.

PbO is used in cathode ray tube glass to block X-ray emission, but mainly in the neck and funnel because it can cause discoloration when used in the faceplate. Strontium oxide is preferred for the faceplate.