Chapter 12.1 - Properties of alkanes

Question 1

What are alkanes most used for?

Answer 1

As fuels(natural gas and crude oil) due to their reaction with oxygen to generate heat

Question 2

Describe the bonding in alkanes

Answer 2

• Saturated hydrocarbons containing only carbon and hydrogen atoms joint together by single covalent bonds(sigma bonds)
• Each carbon atom is bonded to four other atoms

Question 3

Define the term sigma bond

Answer 3

A bond resulted from the axial overlap of two elecrton s orbitals, one from each bonding atom
- Each electron is in the s orbital

Question 4

Describe the shape of alkanes

Answer 4

• Tetrahedral arrangement
• 109.5° bond angle

Question 5

Explain the variation in the boiling points of alkanes

Answer 5

• Boiling point increases with increasing chain length
• This is due to the intermolecular london forces
• They hold the molecules together
• The greater the number of molecules, the greater the london forces and so the higher the boiling point

Question 6

Explain the effect of chain length on boiling point

Answer 6

1. Longer chain alkanes have greater boiling points
2. The larger the chain length, the greater the surface area, and so the greater the surface points of contact
3. So there are more/ stronger london forces
4. To overcome them, a higher supply of energy is required, therefore they have high boiling points

Question 7

Explain the effect of branching on boiling point

Answer 7

1. Branched chain alkanes have lower boiling points
2. Branched chains means that the alkane has fewer surface points of contact between the molecules
3. So there are fewer london forces
4. And so a fewer supply of energy is required to overcome them, therefore they have low boiling points