describe what happens to sulphur as it is heated from room temperature to about 250 degrees c mention the various allotropes encountered.
http://en.m.wikipedia.org/wiki/Allotropes_of_sulfur
As sulfur is heated from room temperature to about 250 degrees Celsius, it undergoes several allotropic transformations. Allotropy is the phenomenon where an element can exist in different physical forms with distinct crystal structures and properties.
Initially, at room temperature (~25 degrees Celsius), sulfur exists in its most stable and common form known as rhombic sulfur or α-sulfur. Rhombic sulfur consists of yellow, crystalline particles arranged in a rhombic lattice structure.
As the temperature increases, around 95.6 degrees Celsius, α-sulfur undergoes a phase transition to another allotrope called monoclinic sulfur or β-sulfur. This transition is accompanied by a change in the crystal structure, resulting in a form of sulfur with needle-like crystals. β-sulfur is still yellow but appears denser than α-sulfur.
Continuing to heat sulfur, around 119 degrees Celsius, β-sulfur transforms into yet another allotrope called plastic sulfur or γ-sulfur. This transition results in the conversion of the needle-like crystals into a more amorphous or rubbery appearance. Plastic sulfur is characterized by a translucent yellow color.
Further heating leads to the final transformation, occurring around 160 degrees Celsius, to a highly reactive and unstable form referred to as amorphous sulfur or ρ-sulfur. Amorphous sulfur lacks a well-defined crystal structure and instead appears as a brownish-black powder or glassy solid.
Once sulfur reaches about 250 degrees Celsius, it starts to vaporize, turning into a yellowish gas composed of S8 molecules, which is the elemental sulfur we commonly associate with its distinct odor.
To summarize, as sulfur is heated from room temperature to about 250 degrees Celsius, it sequentially transforms from α-sulfur (rhombic sulfur) to β-sulfur (monoclinic sulfur), then to γ-sulfur (plastic sulfur), and finally to ρ-sulfur (amorphous sulfur) before vaporizing as a gas.