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 

Allotrope is the ability of an element to exist in two or more different forms in the same physical state. 

Allotropy is the phenomenon whereby an element exist in two or more different forms in the same physical state. 

The main allotropes of sulphur are:

1. Rhombic Sulphur (α- Sulphur)

2. Monoclinic or prismatic Sulphur (β-Sulphur)

3. Amorphous Sulphur (δ- Sulphur)

4. Plastic Sulphur

NOTE: Rhombic and monoclinic sulphur are the Crystalline forms 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

Amorphous sulphur is a non-crystalline form of sulphur. It does not have a definite geometrical shape like crystalline sulphur.

              Physical Properties

1. It is dark brown or black in colour.

2. It is soft and elastic in nature.

3. It has no definite crystal shape.

4. It is insoluble in water.

5. It is slightly soluble in carbon disulphide.

6. It is unstable and gradually changes to rhombic sulphur on standing.

7. It has a lower density than crystalline sulphur.

                 Plastic Sulphur

Plastic sulphur is an amorphous form of sulphur obtained by pouring molten sulphur into cold water.

                Physical Properties

1. It is dark brown or black in colour.

2. It is soft and rubber-like (elastic).

3. It is amorphous, meaning it has no definite crystal shape.

4. It is insoluble in water.

5. It is less stable than rhombic sulphur.

6. It has no sharp melting point.

7. It gradually changes back to rhombic sulphur on standing.

      Physical Properties of Sulphur 

1. Sulphur is a yellow solid. It exists in two forms: amorphous and crystalline 

2. It is insoluble in water but soluble in carbon (IV) sulphide and methylbenzene (toluene)

3. Sulphur is a bad conductor of heat and electricity 

4. Its density depends on the allotropic form

5. It has a melting point of 119°C and a boiling point of 444°C