Tin is a malleable, ductile, highly crystalline, silvery-white metal; when
a bar of tin is bent, a strange crackling sound known as the "tin cry"
can be heard due to the breaking of the crystals. This metal resists
corrosion from distilled, sea and soft tap water, but can be attacked by
strong acids, alkalis, and by acid salts. Tin acts as a catalyst when oxygen
is in solution and helps accelerate chemical attack. Tin forms the dioxide
SnO2 when it is heated in the presence of air. SnO2, in turn, is feebly
acidic and forms stannate (SnO3-2) salts with basic oxides.
Tin's chemical properties fall between those of metals and non-metals, just
as the semiconductors silicon and germanium do. Tin has two allotropes at
normal pressure and temperature: gray tin and white tin.
Below 13.2 °C, it exists as gray or alpha tin, which has a cubic
crystal structure similar to silicon and germanium. Gray tin has no metallic
properties at all, is a dull-gray powdery material, and has few uses, other
than a few specialized semiconductor applications.
Zinc is a moderately-reactive bluish-white metal that tarnishes in moist
air and burns in air with a bright bluish-green flame, giving off plumes of
zinc oxide. It reacts with acids, alkalis and other non-metals. If not
completely pure, zinc reacts with dilute acids to release hydrogen. The one
common oxidation state of zinc is +2. From 100 °C to 210 °C zinc
metal is malleable and can easily be beaten into various shapes. Above 210 °C,
the metal becomes brittle and will be pulverized by beating.