How well do you know your Fe from your Cu, and what the heck is Np? Brian Cox and Robin Ince are joined by comedian Katy Brand, Prof Polly Arnold and Prof Andrea Sella to celebrate the 150th anniversary of Dmitri Mendeleev's great achievement. They find out how scientists first realised that the elements that form the ingredients that make up our planet , are able to be organised in such a logical and ordered way, and whether its still a useful tool today. They also discover why one of the guests has been called the Free Solo equivalent of chemists because of the skill and danger involved in their work.