Properties of Alkenes

Question 1

What is the general formula of alkenes?

Answer 1

C_nH_2n

Question 2

Draw a diagram to show how Pi-bonds form when two orbitals n the carbon atom overlap

Answer 2

A picture of an alkene with two pi bond
The pi bonds overlap sideways froming a pi-bond

Question 3

Name the two covalent bonds in the double bond of alkenes

Answer 3

• Sigma bond
• Pi bond

Question 4

Which is more reactive sigma bond or pi bond?

Answer 4

Sigma bond

Question 5

Why is the pi bond less reactive than the sigma bond

Answer 5

1. It has a lower bond enthalpy due to the sideways overlap of P-orbitals rather than direct overlap
2. This means less energy is required to break pi bonds

Question 6

Give two reasons why alkenes have a high reactivity

Answer 6

1. The double bond is a region of high electron density
2. The double bond contains a pi bond which has a low bond enthalpy due to sideways overlap of orbitals and so little energy is required to break the pi-bond

Question 7

Name the shape of the bond around C atoms in alkenes

Answer 7

Trigonal planar

Question 8

Give the bond angle around each C atom in alkenes

Answer 8

120 degrees

Question 9

Give the reason for the shape and bond angle aroud each C atom in alkenes

Answer 9

There are three bonded electorn pairs around each carbon atom.
The electron pairs repel eachother equally, forming a trigonal planar shape and bond angle of 120 degrees