GROUP 14: TIN AND LEAD

Tin and lead give some resemblance to the lighter elements in group 14, especially Ge. Although they are uniquely more metallic in their physical and chemical characteristics, simple cationic chemistry is the exception rather than the rule. As with group 13, two oxidation states MIV and MII are found, the MII form giving more stable for lead.

Both substances have rather low abundance, but are commoner than other heavy metals. They occur in the minerals galena PbS and cassiterite SnO2. They each have various stable isotopes, Sn more than any other element (10). Some Pb isotopes are discovered from the radioactive decay of uranium and thorium. The isotopic composition of Pb (and thus its atomic mass) differs detectably according to the source, and such variations have been used to estimate the age the Earth of and of rocks.

The elements are readily made by reduction of their ores and are soft, low-melting, somewhat unreactive metals. Tin is required for plating, and both elements in low-melting alloys and as many elements. Applications of lead are declining as its substances are very toxic. A continuing major need is in leadacid batteries, which depend on two reactions involving the PbII, Pb0 and PbIV states:

Occurring at different electrodes, these show a cell potential of 2 V, greater than can be obtained easily from any other pair of electrode reactions in aqueous solution