How do nuclear bombs work?

Question: How do nuclear bombs work?
- Keywords:
  nuclear
Asked by Zealousy to Rob on 19 Jun 2015. This question was also asked by stuff.
- Rob Temperton answered on 19 Jun 2015:
  
  There are two types of nuclear reactions used in bombs. These are:
  
  – Fission. Heavy elements split apart releasing energy.
  – Fusion. Light elements join together releasing lots of energy.
  
  The aim of atoms in life is to minimise their energy state. Therefore atoms will combine or split in a way to achieve this. It doesn’t happen all around us because you need to put energy in in order to get over a kind of energy barrier to allow the process to happen. The most stable nuclei are medium sized elements – things around the size of iron which has an atomic mass of 56. This is a reason why there is a lot of iron in the universe as it is pretty much the most stable (lowest energy nucleus) that is possible.
  
  Rob

Question: How do nuclear bombs work?