What has been the most influential chemistry discovery?

The discovery of the atom, and the nature of the inter-atomic bond. 

Richard Templer, head of chemistry, Imperial College London, UK

A Synthetic polymers - in the last 100 years they have changed everything we know and have a component in everything from ballistic protection, electronics, medicine, and synthetic biomolecules. 

Timothy Swager, head of chemistry, Massachusetts Institute of Technology, US 

A There is no simple, single answer to this question. Chemistry is a vast and boundless subject where every part, from the deepest theory to the most complex application, impacts upon every other part. Any reasoned answer to this question, which is not contrived, would fill many whole issues of Chemistry World.

Charles Rees, professor of chemistry, Imperial College London, UK

A The molecular structures of matter. 

Guy Orpen, head of chemistry, University of Bristol, UK