Question 1

What happens during polymerisation of ethene?

Accepted Answer

Ethene molecules open their C=C double bonds and join through new sigma bonds. The result is polythene, whose repeat unit is -CH2-CH2- and whose backbone is saturated.

Question 2

Why is the repeat unit of polythene written as -CH2-CH2-?

Accepted Answer

Each ethene molecule contributes two carbon atoms to the polymer chain. Addition polymerisation does not remove atoms from the monomer, so those two carbons carry four hydrogens in the repeating saturated unit.

Question 3

Is any small molecule released during ethene polymerisation?

Accepted Answer

No. This is addition polymerisation, so no small molecule is eliminated. The pi electrons help form new sigma bonds while the monomer atoms are retained in the polymer chain.

Question 4

What is the difference between the sigma and pi parts of a C=C bond?

Accepted Answer

The sigma bond is the direct head-on overlap between the two carbon orbitals. The pi bond is formed by sideways overlap of parallel p orbitals oriented perpendicular to the molecular plane.

Question 5

How can you count carbon and hydrogen atoms in polythene?

Accepted Answer

For n repeat units, there are 2n carbon atoms and 4n hydrogen atoms. Thus, 3 units contain C6H12 and 6 units contain C12H24.

Polymerisation 3D Lab - Ethene se Polythene

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