Sulphur preparation and properties, Group 16 P Block Elements
It is the second member of group – 16 It is a typical non-metal. Its atomic number is 16 and electronic configuration is 1s2 2s2 2p6 3s2 3p4.
→ Sulphur occurs in the earth’s crust to extent of 0.06%. It coeurs in nature in both combined and free states. In free state it is found in the volcanic regions of Japan, South America. Sicily and Russia..
→ In combined state, it exist in the form of sulphates and sulphides. Some example are given below
- Epsom salt (MgSO4 . 7H2O)
- Galena (PbS)
- Copper pyrites (CuFeS2)
- Iron pyrites (Fes2)
- Zinc blende (ZnS)
- Cinnabar (HgS)
- Gypsum (CaSO4 . 2H2O)
- Barytos (BaSO4)
→ Traces of sulphur also occurs as hydrogen sulphide (H2S) gas coming out from the volcanoes. Some organic substances like proteins, hair, onion, eggs, garlic, wool etc, also have small percentage of sulphur.
Allotropes of Sulphur
exhibit in various allotropic forms. The various allotropes of sulphur are discussed below.
→ Orthorhombic or Octahedral or c-Sulphur or Yellow sulphur or Rhombic Sulphur: It is a common form of sulphur. It can be prepared when the solution of sulphur in carbon-di-sulphide (CS2), taken in a dish, is evaporated slowly then crystals of sulphur are appeared in dish.
→ It is most stable and common allotropic form of sulphur. It is yellow in colour. It a melting point is 386.8KIts specific gravity is 2.06 pem! It is insoluble in water but soluble in benene, akohol and other. It is highly soluble in carbon di sulphide, it has very little electrical and thermal conductivity. It exist as S, molecule which has puckered ring like or crown shaped structure.
→ Monoclinic or prismatie ors-Sulphur : Monoclinic sulphur is prepared by melting the sulphur ina china dish and cooling till the crust is formed. On removing the crust needle shaped crystals of monoclinic sulphur are obtained.
→ This allotropic form of sulphur is dull yellow in colour. Its specific gravity is 1.98 g/cm3. Its melting point is 393 K. It is insoluble in water but soluble only in carbon disulphide (CS2), It slowly changes into rhombie sulphur. It also exist ass, molecule with puckered ring like or crown shaped structure but it differs from the rhombic sulphur in the symmetry.
In contrast, below 360 K temperatured-sulphur is stable. This temperature is known as transition temperature.
→ Plastic Sulphur or Amorphous sulphur or y Sulphur : When molten sulphur is poured into cokl water then soft rubber like mass is obtained which is known as plastie sulphur. This super cooled liquid is insoluble in water as well as carbon disulphide (CS2). It i anamorphous form of sulphur. It has no sharp melting point. Its specific gravity in 1.95 g/cm3. It has zig-zag chain like structure.
→ Colloidal Sulphur or & Sulphur It can be obtained from any oxidising agent or sodium thio sulphate. When sodium thiosulphate reacts with dilute hydrochloric acid then colloidal sulphur is obtained.
→ Cyclo S6-20 form : In this form sulphur exist as a ring where S6 occupy a chair form. Cyclo-S6 form of sulphur is also known as Engel’s sulphur or e-sulphur
→ Catena S(n): It has chain like structure. This allotrope is formed only at high temperature. It exists in liquid state. Sometimes in this form, sulphur exists in vapour phase Here n = 2 – 5.
→ At about 1000K temperature S2 species predominate. Like dioxygen (O2)S2 le paramagnetic and blue coloured. It is due to the presence of unpaired electron in π antibonding molecular orbital.