chapter 12 Flashcards
1
Q
explain alkanes
A
- they are very stable molecules
- main components of natural gas and crude oil
- use fractional distillation to separate crude oil fractions
2
Q
explain sp orbital hybridisation
A
- 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
3
Q
what is a sigma bond
A
- 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
4
Q
what is the effect of chain length on boiling points
A
- 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
5
Q
effect of branching on boiling point
A
- 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
6
Q
what is homolytic fission
A
- 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
7
Q
what is heterolytic fission
A
- one of the bonded atoms take both of the electrons from the bond
- need a difference in electronegativity
- ions are created
8
Q
what are addition reactions
A
- two reactant molecules join together to form one product
- 100% atom economy
9
Q
what is a substitution reaction
A
- an atom or a group of atoms is replaced by another atom or group of atoms
10
Q
what is an elimination reaction
A
- a small molecule is removed from a larger molecule
11
Q
explain the chemical reactions of alkanes
A
- 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
12
Q
explain the combustion of alkanes
A
- gives out heat energy
- used as fuel because they are readily available
- if incomplete combustion occurs, carbon monoxide is a product
13
Q
explain the reaction of alkanes with halogens
A
- substitution reaction
- uv radiation is required to start the reaction
- bond breaking is endothermic
14
Q
what is initiation
A
- formation of radicals
- requires energy
15
Q
what is propagation
A
- radicals are on both sides of the equations
- starts a chain reaction
16
Q
what is termination
A
- two radicals collide, forming a molecule with all electrons paired
17
Q
what are the limitations to radical substitution
A
- 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
