The modern Atomic Model was first developed by two key scientists Lavoisier and Dalton with the help of others. They formulated the key concepts of the law of conservation of mass and the existence of atoms as the building blocks of all matter using their knowledge of chemical reactions.
A later breakthrough in the discovery of the atomic model came through the work of French chemist Antoine Lavoisier who through a series of experiments found that the total mass of products and reactants in a chemical reactions is always the same. This led to the theory of the law of conservation of mass. This was a crucial breakthrough in the work of atomists in confirming what matter was made of as it was proved that atoms are not created or destroyed when a reaction happens. It also proved the earlier work of Robert Boyle who hypothesised in 1661 that elements cannot be broken down into simpler substances.
The work of Lavoisier and the atomists was furthered in the 18th Century by the British scientist John Dalton. Dalton used the work of Lavoisier and Joseph Proust to examine the ratios of elements that combine to form compounds and look at their ratio of masses. He looked at tin oxide and the combination of masses of oxygen with tin. He found that 100g of tin will combine with 13.5g or 27g of oxygen and that this could be represented by a 2:1 ratio, for every 2 atoms of oxygen there was one atom of tin. This built on the work of Lavoisier and Dalton furthered this proposing that each chemical element is made of atoms of a unique type and they cannot be altered or destroyed but can be combined. Through different experiments with gases Dalton expanded on this to theorise that atoms vary in size and mass and that compounds had to be made of whole number ratios of atoms.
Atomists is the term given to the philosophers over time who believed in the theory and school of though the of the Ancient Greek philosophers Leucippus and Democritus
John Dalton was an English chemist who proposed the idea of the atom as the smallest part of matter and studied gas ratios to prove its existence
Antoine Lavoisier was a French chemist conducted many experiments on gases and discovered the role of oxygen in combustion, from this work he devised the law of conservation of mass. He also discovered many new elements
Joseph Proust was French chemist who discovered that chemicals combine in whole number ratios. His work was mainly done reacting tin and other metals with oxygen
The law of conservation of mass was devised by Antoine Lavoiser who discovered that when you react elements together to form compounds no mass is lost or gained between reactants and products
Robert Boyle was an English philosopher who is considered as the first chemist due to his experimental techniques who discovered the link between changing a gases pressure and its volume.