Module 4: Alkanes Flashcards
1
Q
Why do alkanes have a tetrahedral shape?
A
- Each carbon bonds have four bonding pairs of electrons and they repel equally
- Angle is 109.5
2
Q
Explain the bonding in alkanes
A
- Sigma bonds are formed by the carbon and hydrogen atoms overlapping which allows rotation
3
Q
What are the properties of sigma bonds?
A
- Have high bond enthalpy because of the high electron density of the nuclei resulting in a strong electrostatic attraction
4
Q
Explain the boiling point trend in alkanes
A
- Longer the chains, the greater the boiling point as there is more contact and more induced dipole-dipole interactions
- Increase the branching reduces the boiling point due to the weak induced dipole-dipole forces and small contact area
5
Q
Why are alkanes unreactive?
A
- The sigma bonds are very strong and very hard to break
- The sigma bonds are non-polar so they won’t attract any uncharged particles
6
Q
Explain the combustion in alkanes
A
- Goes under complete combustion and forms carbon dioxide and water
- Alkanes are good fuels which is used to power vehicles and electricity
7
Q
What are the issues with incomplete combustion?
A
- Carbon monoxide is produced which is very toxic and can bond with the haemoglobin which prevents oxygen bonding
- Soot is formed which can cause breathing problems
8
Q
How is haloalkanes formed from alkanes?
A
From radical substitution
9
Q
What is the first step of radical substitution?
A
- Initiation
- Radicals are produced by photodissociation (sunlight providing energy to break bonds)
- Homolytic fission is used
10
Q
What happens during the propagation stage?
A
- Radicals are used up and creates a chain reaction
- The chlorine radical attacks the methane and produces are methyl radical which goes and attacks another chlorine molecule
11
Q
What happens at the end of the chain reaction?
A
- 2 radicals collide and produces a non-radical
12
Q
Explain the limitation of radical substitution
A
Unwanted products are formed which have to be seperated by adding excss methane
