Antoine Lavoisier

Lavoisier came from French nobility and used his position on aristocratic councils and as an administrator of the Ferme générale - the ancien régime's most hated tax apparatus - to bankroll his laboratory work. Through more precise measurement than his predecessors, he confirmed that mass stays constant in closed systems even as matter changes form, laying the ground for balanced equations. He discovered oxygen's role in combustion in the 1770s, named it in 1778, recognized hydrogen as an element in 1783, helped construct the metric system, and wrote the first extensive list of elements in 1787, predicting silicon's existence. His wife and laboratory assistant, Marie-Anne Paulze Lavoisier, became a renowned chemist and worked beside him on the metric reforms. When the Revolution came, his aristocratic ties and role in tax collection caught up with him: charged with fraud and selling adulterated tobacco, he was guillotined on 8 May 1794 despite appeals to spare him for his scientific contributions. Eighteen months later, the government exonerated him.