Bonding, Alkenes, Isomers

Question 1

What are the two types of bonds?

Answer 1

Pi and Sigma bonds

Question 2

What is more common Pi or Sigma?

Answer 2

Sigma bonds

Question 3

What is a sigma bond?

Answer 3

Sigma bonds are the strongest type of covalent bond. All single bonds and the first part of double or triple bonds are sigma bonds

Question 4

What is a Pi bond?

Answer 4

The second and third part of a triple bond or the second part of a double bond. The Pi bond is not directly between the nuclei so is weaker than a Sigma bond.

Question 5

What do the solid and dashed wedges represent when it comes to representing a 3D molecule

Answer 5

-wedges are the bonds going away from the plane of the paper
-dashes are the bonds coming towards the plane of the paper

Question 6

How does Ethene become 1,2-dibromoethane?

Answer 6

Through electrophilic addition at room temperature and pressure when Bromine (aq) is added to ethene

Question 7

How does ethene become 1chloroethane when HCl (aq) is added?

Answer 7

Through electrophilic addition under RTP and the addition of HCl (aq)

Question 8

What two ways does ethene become ethane?

Answer 8

1. Through addition with an Ni catalyst and H2 (g) at High temperature and pressure
2. With a Pt catalyst and H2 (g) at room temperature and pressure

Question 9

How does ethene become ethanol?

Answer 9

Through electrophilic addition with the H3PO4 and H2O (g) at high temperature and pressure

Question 10

Describe alkenes reactions with halogens

Answer 10

Alkenes react with halogens at RTP.

Question 11

Describe the Bromine test for halogens

Answer 11

• add a few drops of bromine water Br2(aq) to an alkene and shake well
• if the compound contains a carbon carbon double bond (unsaturated) there will be a colour change from orange to colourless

Question 12

Describe the electrophilic addition mechanism

Answer 12

1. The partially positive bromine atom accepts a pair of electrons from the carbon carbon double bond
2. The Br-Br bond breaks
3. This leaves a carbocation intermediate which is unstable and quickly reacts with the Br- from the broken Br-Br bond
   The final product is formed

Question 13

Define electrophile

Answer 13

An electrophile is a positive ion or molecule with a partially positive region which is attracted to a negative region in a molecule, which reacts by accepting a pair of electrons forming a covalent bond.

Question 14

Define addition reaction

Answer 14

Addition reactions are when 2 molecules react to give just 1 product molecule (by combining together)

Question 15

What would happen if an unsymmetrical alkene was used in an electrophilic addition reaction (like propene)?

Answer 15

There would be two products on two/ or more different carbons

Question 16

How can converting an alkene into an alkane be used?

Answer 16

• to find out how many double bonds an alkene has
• hydrogenation of vegetable oils to convert them into margarine since carbon carbon bonds have a higher mp than carbon carbon double bonds

Question 17

What are the two types of isomerism?

Answer 17

-structural isomers molecules with the same molecular formula but different structural formulas
-steroisomerism molecules with the same molecular formula but atoms point a different way in space (E/Z isomerism)

Question 18

MAGIC SENTENCE
What is required for a molecule to have E/Z isomerism?

Answer 18

• a carbon carbon double bond which cannot rotate
• each carbon in the carbon carbon double bond must be bonded to 2 different atoms or groups