13.1 The properties of the alkenes

Question 1

What are alkenes

Answer 1

Unsaturated hydrocarbons

Contain at least one carbon to carbon double bond

Question 2

What is the general formula for the aliphatic alkenes that contain one double bond

Answer 2

CnH2n

Question 3

What is the general formula for branched alkenes

Answer 3

CnH2n

Question 4

Do cyclic alkenes and alkenes with more than one double bond follow the CnH2n general formula

Answer 4

NONONO

Question 5

How are the carbon atoms bonded

Answer 5

Three of the four electrons are used in three σ- bonds; one to the other carbon atom of the double bond and the other two to two other atoms leaving one not involved in sigma bonds
This electron is in a p-orbital, a π-bond

Question 6

How is a π-bond formed

Answer 6

By the sideways overlap of two p-orbitals, one from each carbon atom of the double bond
Each carbon atom contributes one electron to the electron pair in the π-bond. The π-electron density is concentrated above and below the line joining the nuclei of the bonding atoms

Question 7

What does a V-bond do

Answer 7

Locks the two carbon atoms in position and prevents them from rotating around the double bond.
Makes the geometry of the alkenes different from that of the alkanes where rotation is possible around every atom

Question 8

What is the shape around each of the carbon atoms in the double bond

Answer 8

Trigonal planar

Question 9

Why is the shape around each of the carbon atoms in the double bond trigonal planar

Answer 9

There are three regions of electron density around each of the carbon atoms
The three regions repel each other as far apart as possible so bond angle is 120
All of the atoms are in the same place

Question 10

What makes flamingos pink

Answer 10

Alkenes
Flamingos eat algae and crustaceans containing carotenoids
Enzymes in liver convert these into pink and orange pigments deposited in feathers