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400 BCE
Democritus
He was the first one to say that everything was made of particles called atoms. -
300 BCE
Aristotle
He believed that everything was made out of "The Four Elements" including Fire, Earth, Air, and Water. -
Lavoisier
He discovered that matter cannot be destroyed or created during a chemical or physical change. It can only be transformed. He created the Law of Conservation of Matter. -
Dalton
He created the Dalton's Atomic Theory that states that all matter is made of atoms, matter is indestructible, it cannot be divided into smaller particles, and all elements are exactly alike. He also created a theory behind the Law of Definite Proportions stating that if matter is composed of indivisible atoms, then a chemical reaction would only rearrange these atoms and no atoms would be created or destroyed. -
Avogrado
He discovered that equal values of all gases at the same temperature and pressure contain equal numbers of molecules. -
Berzelius
He made a table of atomic weights that included 43 elements. -
Mendeleev
He discovered the organization and patterns in the chemical and physical properties of the elements when they are arranged by atomic mass. He developed the Periodic Table of Elements and published it in 1869. -
Becquerel
He was the first one to discover evidence of radioactivity. -
Thomson
He discovered that the solid ball model was incorrect by figuring out that there were positive and negative charges in the atom. He made a model with this new data and called it the Plum Pudding Atomic Model. -
Curie
She studied the radiation of compounds with known radioactive elements in them and discovered that the compounds were also radioactive. She measured the strength of radiation and figured out that the ability to emit radiation did not depend on the arrangement of atoms. Also, in her studies, she discovered two new radioactive elements: radium and polonium. -
Rutherford
Rutherford was the scientist that ran the Gold Foil Experiment. He fired protons at foil and discovered the existence of the nucleus through his experiment. He created the Rutherford Model. -
Bohr
He created the Bohr Planetary Model that included the theory that electrons orbit around the nucleus like planets since gravity pulls into the nucleus so the electrons must keep moving and orbit around the nucleus so they don't get pulled into the nucleus. -
Moseley
He studied the atomic structure with an x-ray spectrum that he invented. He developed a more accurate way of organizing the periodic table by finding more precise atomic numbers. -
Millikan
He studied the electric charge carried within a single electron with his oil drop experiment. He also studied the radiation from outer space and proved Albert Einstein's law on the photoelectric effect. -
Schrodinger
He figured out that the electrons in atoms had wave like orbits around the atom. He called his model the Electron Cloud Model. -
Heisenberg
Heisenberg proposed the Principle of Indeterminacy that says that it is impossible to accurately measure both the position and momentum of a small particle at the same time. He also discovered that electrons have photons. -
Chadwick
He discovered that there were neutrons in the nucleus and they have a neutral charge. -
Meitner
She researched beta and gamma rays with radioactivity and invented nuclear fission. She discovered that heavy elements capture neutrons and form unstable products to cause fission. She found out how to split the nucleus of the atom. -
Planck
He established the quantum theory where energy can only be absorbed or radiated in certain amounts labeled as quanta.
