Physical and chemical properties of tin

Metallic tin is soft, easy to bend, with silver-white metallic luster, melting point 231.89℃, boiling point 2260℃, non-toxic. Tin belongs to the fourth major element in the periodic table, atomic number 50, atomic weight 118.71, element symbol Sn, tin is malleable at room temperature. Especially at 100 ° C, the malleability is very good and can be developed into extremely thin tin foil, which can be as thin as 0.04 mm or less. But the ductility is very poor, a pull will be broken, can not be drawn into a fine wire.

At the same time, tin is a metal that is afraid of both cold and heat, and the shape of tin is completely different at different temperatures.

Tin in the temperature range of 13.2 ~ 161 ° C, the nature of tin is the most stable, called "white tin".

When the temperature drops below 13.2 ° C, tin will gradually turn into a loose powder like coal ash. Especially at -33℃ or in the presence of red salt (SnCl4•2NH4Cl) alcohol solution, the speed of this change is greatly accelerated. This "disease" of tin can also be transmitted to other "healthy" tin, and as long as the white tin hits the gray tin, even if it hits a little, the white tin will quickly and completely change into gray tin. The phenomenon was called the tin epidemic. Fortunately, if you melt the diseased tin again, it will recover. The reason for the tin epidemic is that the crystal lattice of tin has changed: at room temperature, tin is a square crystal structure, called white tin. When you bend a tin strip, you can often hear a swish sound, which is because the white tin crystals of the square crystal system rub against each other as they bend. Because the tin is afraid of cold, special attention should be paid to avoid freezing the tin in winter. Many iron items welded with tin are also impervious to freezing. In 1912, a foreign Antarctic expedition team went to the Antarctic expedition, the gasoline barrels used were welded with tin, in the Antarctic ice and snow, the solder turned into powder gray tin, and the gasoline all leaked out.

Tin is afraid of heat as well as cold. Above 161℃, white tin is transformed into rhombic tin with a crystal structure of the rhombic system. Rhomboxy tin is very brittle, it breaks when it is knocked, and the malleability is very poor, called "brittle tin".

White tin, gray tin and brittle tin are three allotropes of tin and their respective parameters are as follows:White tin is tetragonal, with cell parameters as follows: a=0.5832nm, c=0.3181nm, 4 Sn atoms in the cell, density 7.28g/cm³, hardness 2;

Gray tin is a diamond-shaped cubic crystal system with cell parameters as follows: a=0.6489nm, 8 Sn atoms in the cell, and a density of 5.75g/cm³.

Brittle tin is an orthorhombic system with a density of 6.54g/cm³.

There are 14 isotopes of tin, 10 of which are stable isotopes: tin 112, 114, 115, 116, 117, 118, 119, 120, 122, 124.

The chemical properties of tin are very stable, and it is not easy to be oxidized at room temperature, so it often maintains a silvery luster. A protective film of tin dioxide is formed on the surface of tin in air, and the oxidation reaction is accelerated under heating condition. Tin tetrahalide is produced by heating reaction between tin and halogen. It also reacts with sulfur; Tin is stable to water, soluble in dilute acid slowly, soluble in concentrated acid faster; Tin can dissolve in strong alkaline solution; It will be corroded in acidic solutions of salts such as ferric chloride and zinc chloride.