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Democritus proposed that matter consisted of indivisible atoms that could not be broken down. In between atoms would be a vacuum.
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Empedocles proposes that air is not nothing and takes up space, creating the Cosmogenic Theory of 4 basic elements
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Aristotle did not believe in vacuums, and added 4 more elements to the cosmogenic theory: hot, dry, wet, and cold. He established the Lyceum in which his science was believed for 2000 years.
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Sir Francis Bacon established the scientific method which is experimentation necessary for all theories.
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Robert Boyle questioned the cosmogenic theory, proposing that an element is a pure substance that could not be broken down, and that elements can combine to create compounds.
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Joseph Priestly discovered oxygen and found that air was a mixture, not a single element. He also believed that elements contained a flammable substance called plogiston.
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Henry Cavendish discovered hydrogen, which mixed with oxygen to create water, proving water is a mixture and not an element.
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Antoine de Lavoisier disproved that elements contained phlogiston, and identified 23 new elements, which were pure substances that could not be broken down. He also established the Law of Conservational Mass which was that matter could not be destroyed.
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Michael Faraday experimented with chemical changes and discovered electricity. He found charged atoms called ions, and proposed that matter had a positive or negative charge. Opposite charges attract holding atoms together, whereas like charges repel.
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JJ Thomson proposed the Plum Pudding model for the atom, proposing a sphere with positive charges, and within the sphere there are negative charges, fitting Michael Farraday's proposal of positive and negative mass
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James Chadwick discovered the neutron which balances out positively charged and negatively charged matter
