13.1 The properties of alkenes

Question 1

What are alkenes?

Answer 1

Unsaturated hydrocarbons, containing at least one C=C double bond in their structure, compromising of a π bond and a σ bond

Question 2

What is the general formula of aliphatic alkenes?

Answer 2

CnH2n

Question 3

How many electrons does carbon have in its outer shell?

Answer 3

4 electrons

Question 4

What is a π bond?

Answer 4

Sideways overlap of adjacent p-orbitals, with electron density concentrated above and below the bonding C atoms

Question 5

How does the π bone affect the alkene ?

Answer 5

Locks two carbon atoms in position and prevents them from rotating around the double bond

Question 6

Where are σ bonds present in alkenes?

Answer 6

For each carbon atom of the double bond, 3 or 4 electrons are used in three σ bonds. 1 to the other carbon atom of the double bond, and the other two electrons to two other atom (carbon or hydrogen)

Question 7

What is the shape around the double bond?

Answer 7

Trigonal Planar

Question 8

Why is the C=C a trigonal planar shape?

Answer 8

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

Question 9

Draw the π and σ bonds around an ethene molecule

Answer 9

Question 10

Which part of the carbon-carbon double bond is the weakest and why?

Answer 10

The π part of the C=C bond is weaker since its electron density is above and below the plane of molecule, whereas the electron density of the σ bond is concentrated between the nuclei, holding them together

Question 12

Draw a diagram for the formation of a 𝛑 bond

Answer 12