Empedocles was the first to propose that four elements that made up everything: earth, wind ,water, and fire. His work later inspired Aristotle.
Democritus was the first person to developed the theory of the atom. His work has been lost and only fragments of his work remain.
Aristotle did not believe in Democritus's atom theory. He believed that all materials on earth were made up of earth, wind, water and fire.
Antoine Lavoisier discovered that mass is retained when it undergoes a chemical reaction. His work led to the law of the law of conservation of matter
John Dalton proposes his atomic theory. The two of his four points in his theory argued that all atoms are indestructible and invisible and a chemical reaction is a rearrangement of atoms.
J.J. Thomson discovered the electron and the proton. He then developed the plum pudding model
Albert Einstein treated energy and matter as the same. This thought process would become known as the theory of relativity
Robert Millikan's oil drop experiment help discover more about the electron. This data helped all future scientist understand the atomic structure.
Marie Curie studied uranium and thorium and called their decay radioactivity. She also discovered elements of polonium and radium
Ernest Rutherford discovered that have a charged nucleus and a space in the middle orbited by electrons. He then came up with the Rutherford
Niels Bohr discovered that there are energy levels for certain electrons. He said that electrons move only in a set orbits
Max Planck devoloped the the quantum theory. This helped scientist understand atoms better
Louise De Broglie did research on quantum physicist. He discovered the wave nature of electrons.
Ernest. Schrodinger created the electron cloud model. It was dense nucleus surrounded by a cloud of electrons
James Chadwick discovered the neutrons are in the center of the atom. They have the same mass as a proton.