SSS 2: Sulphur and its compounds

Sulphur is a chemical element. It has symbol S.

Atomic number of Sulphur=16

Atomic mass of Sulphur=32

Electronic configuration=1s²2s²2p⁶3s²3p⁴

Under normal conditions, sulphur atoms form cyclic octatomic molecules with the chemical formula S_{8 .} 

Sulphur is a bright yellow, crystalline solid at room temperature. It makes up about 0.1% of the earth crust. It is widely found in combined state as sulphide of iron, zinc, lead, copper and mercury. It is also found in some proteins.

                  Extraction of Sulphur

Most of the world's sulphur is obtained from the underground deposits. The process involved in the extraction of Sulphur from the underground is known as FRASCH PROCESS.

                 Allotropes of Sulphur 

The two or more forms of same element having similar chemical properties but different physical properties are called allotropes and the phenomenon is called allotropy.

Sulphur exists in the following allotropic forms:

1. Crystalline forms: Rhombic and monoclinic sulphur 

2. Amorphous forms: Plastic, colloidal and milk of sulphur 

                     Rhombic Sulphur 

1. Rhombic sulphur is crystalline in nature

2. It has bright yellow colour 

3. It is the only stable allotrope of sulphur at temperature below 96°C

4. It has an octahedral shape.

5. It is made up of  S₈ molecules

6. On heating the solution of roll sulphur in carbon (IV) sulphide, [CS₂] we get rhombic sulphur.

7. It has a melting point of 113°C

8. It has a density of 2.08 g/cm³

9. Rhombic sulphur cannot be dissolved in water but can be dissolved in benzene, ether, alcohol etc.

Note: Carbon (IV) sulphide, [CS₂] is poisonous and highly inflammable. Preparation should be done in a fume cupboard.

                     Rhombic sulphur

                    Monoclinic sulphur 

1. Monoclinic sulphur is crystalline in nature

2. It has amber colour 

3. It is the only stable allotrope of sulphur at temperature between 96°C and 119°C

4. It has a thin needle-like shape.

5. It is made up of  S₈ molecules

6. It is obtained by cooling molten sulphur 

7. It has a melting point of 119°C

8. It has a density of 1.98 g/cm³

9. It is less dense than rhombic sulphur. This is because the S₈ molecules in rhombic sulphur is tightly packed.

                     Monoclinic sulphur

                     

                       Amorphous Sulphur

1. Amorphous Sulphur has no regular crystalline shape. 

2. It is prepared as a pale yellow