Full Idea
One of the most influential ideas in modern chemistry is of a covalent bond as a shared pair of electrons (not as transfer of electrons and the formation of ionic bonds).
Gist of Idea
A big chemistry idea is that covalent bonds are shared electrons, not transfer of electrons
Source
Eric R. Scerri (The Periodic Table [2007], 08 'Intro')
Book Reference
Scerri,Eric R.: 'The Periodic Table' [OUP 2007], p.207
A Reaction
Gilbert Newton Lewis was responsible for this.