Question

What is an allotrope ? Explain it with few examples.

Answer 1

    Allotropes are different forms of the same chemical element. Different allotropes have different physical properties. But their chemical properties are exactly the same.

Examples of allotropes of Carbon¹² are: Coal, Diamond, Graphite.

    The crystal structure of the allotropes differ. The distance between the atoms and the arrangement of atoms in the unit crystal are different. So their packing is different. Thus Graphite and diamond are very closely packed compared to Coal. So density is higher.

   Similarly Phosphorus, Sulphur, Oxygen, Semiconductors like Silicon and Germanium also have their allotropes.  We know Dioxygen O2 and Ozone O3 are allotropes of Oxygen. White Phosphorus and Red Phosphorus forms exist too.

Answer 2

Allotropes are defined as the different physical forms of a chemical element. This means the when you observe the structure then you'll notice that the atoms are arranged in different manner.
So due to this they differ in their physical properties but not the chemical properties since the composition remains the same.

Since allotrope of carbon has already been discussed I would like to give example of Sulfur's allotropes i.e Amorphous,Monoclinic ,Orthorhombic.


Let's differentiate the 3 allotropes .

1) Amorphous -

-This is rarely found.
- It is the product of sulfur being melted over 160°C.
- It is large viscosity unlike sulfur.
- The commonly S₈ ring is not seen. Rather it structure contains chains of sulfur.

2) Monoclinic -

- It is crystalline in nature
- It has got S₈ rings.
- It exists between the temperature 96°C - 119°C.
- If the temperature goes below 96°C to changes to more stable allotropic form of sulfur given below.

3) Orthorhombic -

-  Most stable form.
- It has also got S₈ rings.
- It forms below 96°C.

Hope This Helps You