What affects the boiling point of an alkane and why?

There are two ways to affect the boiling point, both of which are to do with London forces found between molecules. Firstly, the chain length. If the chain length increases, the molecules will have a larger surface area, so more surface contact is possible between molecules. This means that the London forces between molecules will be greater and so more energy is required to overcome the forces. As the chain length increases, boiling point increases. Secondly, the amount of branching in the molecule. Branches get in the way and prevent molecules from getting close together, so if there is more branching, there is less surface area of contact which means, just like with chain length, the London Forces are weaker and so less energy is required to overcome the forces. As branching increases, boiling point decreases.