Alkenes

Question 1

what is an alkene?

Answer 1

An alkene is a hydrocarbon with a carbon double bond, and NO rings.

So they are all unsaturated hydrocarbons.

Question 2

what is the general formula of an alkene?

Answer 2

CnH2n

Question 3

what do we call a hydrocarbon that contans a carbon double bond in a ring.

Answer 3

a cycloalkene.

Question 4

are alkenes polar or non polar/ justify your answer.

Answer 4

They are non-polar, because they only contain carbob-carbon, and carbon - hydrogen bonds.

Question 5

describe what happens to melting point as chain length increases.

Answer 5

the number of electrons increases, which means that the wan der waals forces also increase, which means that a greater deal of energy is required to break the bonds, thus higher melting point.

Question 6

describe the solubility of alkenes.

Answer 6

insoluble in water, because they are non-polar.

Question 7

where is there a high region of electron density in an alkene.

Answer 7

in the carbon-carbon double bond.

Question 8

state what is meant by the term stereoisomerism.

Answer 8

when wo molecules have the same molecular formula, but different structural arrangement, we say they are stereoisomers.

Question 9

what is a substituent?

Answer 9

an atom, or group of atoms, which could be replaced by a hydrogen atom.

Question 10

what do we call when an alkene has two substituents on the same side?

Answer 10

Z-isomerism

Question 11

what do we all when an alkene has two substituents on opposite sides?

Answer 11

E - isomerism.

Question 12

describe and explain the test for alkenes.

Answer 12

we add a few drops of bromine solution, which has a brown color. When added to an alkene, it will turn colourless.

• because it acts as an electrophile.

Question 13

state what is menat by the term carbocation.

Answer 13

when a carbon has a positive charge.

Question 14

what is an electrophile?

Answer 14

A substance that accepts electron pairs, in order to form a new covalent bond, is called an electrophile.

Question 15

what are the three chemicals with which alkenes can undergo electrophilic addition.

Answer 15

Br2, HBr, H2SO4.

Question 16

what determines the stability of a carbocation?

Answer 16

How many alkyl groups it is bonded to.

Question 17

describe the trend in stability of positively charged carbon as we go from primary, to tertiary alkenes.

Answer 17

It increases.

Question 18

where is a new bond more likely to form? and explain why.

Answer 18

on the carbon with the most hydrogens bonded to it.

Because the positively charged carbon, wants to be more stable, and it is more stable if it is bonded to two alkyl groups. This is because alkyl groups, donate electron density to the positive carbon, ehich stabalises the carbon more.

Question 19

State what is meant by an addition polymer.

Answer 19

When lots of organic molecules, with lots of organic functional groups, combine to form one macromolecule, we call this addition polymerisation.

Question 20

state and explain the properties of addition polymers.

Answer 20

1. Because they are long, the intermoleular forces between them are very strong, which is why they are tough and rigid.
2. inert, meaning they are unreactive, because of the strong backbone of the polymer, and ebcause they only contain single carbon bonds, and are non-polar.

Question 21

why does polymerisation take place?

Answer 21

because saturated hydrocarbons, are more stable than unsaturated hydrocarbons