Chapter 12 - Alkanes

Question 1

What bond do alkanes have?

Answer 1

Sigma bond (type of covalent bond)

Question 2

What is a sigma bond?

Answer 2

A sigma bond is the result of two overlapping orbitals, one from each bonding atom. Each overlapping orbital contains one electron, so the sigma bond has two electrons that are shared between the bonding atoms

Question 3

How doe boiling point change as chain length of alkanes increases?

Answer 3

As chain length increases, molecules have a larger surface area so more surface contact between molecules and so more and stronger London forces will be acting. This means that the boiling point will increase as chain length increases.

Question 4

How does branching of alkanes affect boiling point?

Answer 4

Branched isomers of the same molecule have a lower boiling point than straight chain isomers of the same molecule. This is because there are fewer points of surface contact between molecules, meaning less London forces. The branch gets in the way and prevents molecules getting as close as straight chain molecules, decreasing intermolecular forces

Question 5

What is produced in the complete combustion of an alkane?

Answer 5

carbon dioxide and water

Question 6

What is produced in incomplete combustion of alkanes?

Answer 6

carbon monoxide and water

Question 7

How do alkanes react with hallogens?

Answer 7

They will only react in the presence of UV light which provides the initial energy for the reaction to take place.
e.g. - CH4 + Br2 –> CH3Br + HBr