208However, it dissolves in nitric and hydrochloric acids, to give elemental sulfur and hydrogen sulfide,
respectively. Upon heating under high pressures with sulfur, it gives the disulfide. In the compound,
the lead atoms are linked octahedrally with the sulfur atoms. It is also a semiconductor. A mixture
of the monoxide and the monosulfide when heated forms the metal.
2 PbO + PbS → 3 Pb + SO 2Halides and Other Salts
Heating lead carbonate with hydrogen fluoride yields the hydrofluoride, which decomposes to the
difluoride when it melts. This white crystalline powder is more soluble than the diiodide, but less
than the dibromide and the dichloride. The tetrafluoride, a yellow crystalline powder, is unstable.
Other dihalides are obtained upon heating lead(II) salts with the halides of other metals; lead
dihalides precipitate to give white orthorhombic crystals (diiodide forms yellow hexagonal crystals).
They can also be obtained by direct reaction of their constituent elements at temperature exceeding
melting points of dihalides. Their solubility increases with temperature; adding more halides first
decreases the solubility, but then increases due to complexation, with the maximum coordination
number being 6.
The complexation depends on halide ion numbers, atomic number of the alkali metal, the halide of
which is added, temperature and solution ionic strength. The tetrachloride is obtained upon
dissolving the dioxide in hydrochloric acid; to prevent the exothermic decomposition, it is kept under
concentrated sulfuric acid. The tetrabromide may not, and the tetraiodide definitely does not exist.
The diastatide has also been prepared.
The metal is not attacked by sulfuric or hydrochloric acids. It dissolves in nitric acid with the
evolution of nitric oxide gas to form dissolved Pb(NO 3 ) 2. It is a well-soluble solid in water; it is thus
a key to receive the precipitates of halides, sulfate, chromate, carbonate, and basic carbonate
Pb 3 (OH) 2 (CO 3 ) 2 salts of lead.
Organolead
The best-known compounds are the two simplest plumbane derivatives: tetramethyllead (TML) and
tetraethyllead (TEL). The homologs of these, as well as hexaethyldilead (HEDL), are of lesser
stability. The tetralkyl derivatives contain lead(IV), where the Pb–C bonds are covalent. They thus
resemble typical organic compounds.
Lead readily forms an equimolar alloy with sodium metal that reacts with alkyl halides to form
organometallic compounds of lead such as tetraethyllead. The Pb–C bond energies in TML and
TEL are only 167 and 145 kJ/mol; the compounds thus decompose upon heating, with first signs
of TEL composition seen at 100 °C (210 °F).
The pyrolysis yields of elemental lead and alkyl radicals; their interreaction causes the synthesis of
HEDL. TML and TEL also decompose upon sunlight or UV light. In presence of chlorine, the alkyls
begin to be replaced with chlorides; the R 2 PbCl 2 in the presence of HCl (a by-product of the
previous reaction) leads to the complete mineralization to give PbCl 2. Reaction with bromine follows
the same principle.