Allotropes of Sn (tin)

Some of the chemical elements exist in more than one different structural forms maintaining the same physical state. These different forms of a single element within the same phase are known as allotropes or allotropic forms and the property by virtue of which allotropes are formed is known as allotropy or allotropism. All the allotropes of an element exist with the same building block,  but the way in which the  building blocks are arranged in these forms are different. In other words, they have distinct crystalline forms. It should be noted that the term allotropy is used for elements only and not for compounds.

Allotropes of Sn

When a bar of tin is bent, a crackling sound known as the "tin cry" can be heard from the twinning of the crystals. Tin melts at the low temperature of about 232 °C (450 °F), the lowest in group 14.

1) Alpha or Grey Tin

Tin exists in this form at low temperatures, below 13.2°C. It has a cubic crystal structure similar to silicon and germanium.

2) Beta or White Tin

Tin exists in this form when heated above 13.2°C. It is metallic and has a tetragonal structure. It slowly changes back to the gray form when cooled, which is called the "tin pest" or "tin disease". However, this transformation is affected by impurities such as aluminium and zinc and can be prevented from occurring through the addition of antimony or bismuth.

β-tin (the metallic form, or white tin), which is stable at and above room temperature, is malleable. In contrast, α-tin (nonmetallic form, or gray tin), which is stable below 13.2 °C (55.8 °F), is brittle. α-tin has a diamond cubic crystal structure, similar to diamond, silicon or germanium. α-tin has no metallic properties at all because its atoms form a covalent structure in which electrons cannot move freely. It is a dull-gray powdery material with no common uses other than a few specialized semiconductor applications.These two allotropes, α-tin and β-tin, are more commonly known as gray tin and white tin, respectively. In cold conditions, β-tin tends to transform spontaneously into α-tin, a phenomenon known as "tin pest" or tin disease.