chapter 12

Question 1

explain alkanes

Answer 1

• they are very stable molecules
• main components of natural gas and crude oil
• use fractional distillation to separate crude oil fractions

Question 2

explain sp orbital hybridisation

Answer 2

• when the s and the p orbitals in carbon gain enough energy they merge together
• this creates 4 bonding electrons for carbon
• they become sp3 hydrolysed orbitals

Question 3

what is a sigma bond

Answer 3

• direct overlap of atomic orbitals directly between the bonding atoms
• each bond is a shared pair of electrons
• each bond is positioned on a line directly between the bonding atoms
• they can rotate around each bond

Question 4

what is the effect of chain length on boiling points

Answer 4

• chain length increases = larger surface area
• more surface contact is possible between the molecules
• London forces between molecules will be greater
• more energy is needed to overcome these forces

Question 5

effect of branching on boiling point

Answer 5

• as branching increases, there is less surface contact leading to fewer London forces
• molecules get further away from each other leading to weaker London forces
• less energy is required to overcome these forces

Question 6

what is homolytic fission

Answer 6

• each of the bonded atoms takes one of the shared pair of electrons from the bond
• radicals are created
• radicals = contain unpaired electrons and they are extremely reactive

Question 7

what is heterolytic fission

Answer 7

• one of the bonded atoms take both of the electrons from the bond
• need a difference in electronegativity
• ions are created

Question 8

what are addition reactions

Answer 8

• two reactant molecules join together to form one product
• 100% atom economy

Question 9

what is a substitution reaction

Answer 9

• an atom or a group of atoms is replaced by another atom or group of atoms

Question 10

what is an elimination reaction

Answer 10

• a small molecule is removed from a larger molecule

Question 11

explain the chemical reactions of alkanes

Answer 11

• very stable molecules
• crude oil proves this
• sigma bonds are very strong so they don’t tend to brake
• they are non polar
• they need high energy to break

Question 12

explain the combustion of alkanes

Answer 12

• gives out heat energy
• used as fuel because they are readily available
• if incomplete combustion occurs, carbon monoxide is a product

Question 13

explain the reaction of alkanes with halogens

Answer 13

• substitution reaction
• uv radiation is required to start the reaction
• bond breaking is endothermic

Question 14

what is initiation

Answer 14

• formation of radicals
• requires energy

Question 15

what is propagation

Answer 15

• radicals are on both sides of the equations
• starts a chain reaction

Question 16

what is termination

Answer 16

• two radicals collide, forming a molecule with all electrons paired

Question 17

what are the limitations to radical substitution

Answer 17

• further substitution = we cannot control when the reaction will stop, dihaloalkanes could form and this substitution will continue until all the hydrogen atoms have been replaced
• substitution at different points along the carbon chain