13.1 - Properties of Alkenes

Question 1

What is the general formula of an alkene?

Answer 1

CnH2n (aliphatic with C=C bonds)

Question 2

How is the double bond formed?

Answer 2

Per carbon atom of the double bond,
- 3 of the 4 electrons are sigma bonded to the other carbon and the rest hydrogens
(1st bond with any atom is a sigma bond)

• The 4th electron is in the p-orbital and forms a pi bond
• The 2 p orbitals on each carbon overlap to form the pi bond

Question 3

What are the properties of the pi bond?

Answer 3

Each carbon atom bonds one electron to the pair
The pi-electron density is concentrated above and below the bond.

• It is rigid and locks the C=C in place not allowing any rotation

Question 4

What is the shape around the double bond?

Answer 4

• Due to electron repulsion and the 3 regions of electron density…
• Trigonal planar - all atoms on same plane
• 120 degrees bond angle, the bond angles that arent’t around the C=C are 109.5