Alkanes - Properties of the Alkanes

Question 1

What is a hydrocarbon?

Answer 1

A compound made up of carbon & hydrogen only.

Question 2

Describe + explain the arrangement of bonds around each carbon atom in an alkane.

Answer 2

• Each C atom in an alkane forms four single bonds, either with H atoms (C-H) or other C atoms (C-C).
• These bonds are arranged in a tetrahedral geometry around the central C atom, with bond angles of 109.5°.
• The tetrahedral arrangement of the bonds is due to the equal repulsion between the bonding pairs of electrons.

Question 3

State + explain the effects of increasing chain length on the boiling points of alkanes.

Answer 3

• As chain length increases, boiling point increases.
• Surface contact between molecules increases which leads to stronger london forces between molecules which require greater energy to overcome.

Question 4

State + explain the effect of branching on the boiling points of alkanes.

Answer 4

• Branched alkanes have lower boiling points than straight-chain isomers.
• Branched alkanes can’t pack as closely together which means there are fewer surface points of contact. This leads to weaker london forces which require less energy to overcome.

Question 5

What is a sigma (𝛔) bond?

Answer 5

Type of covalent bond that is formed when 2 atomic orbitals overlap directly between the 2 bonding atoms, allowing electrons to be shared between them.