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340
Aristotle
Aristotle was one of the first contributors to the atomic theory and had ideas that were thought to be true for thousands of years. He proposed that everything was made of either earth, wind, fire, or water. The picture displays how each texture of object could be created by combining two of the elements. -
400
Democritus
The very first person to suggest atomic theory. He named the atom as atomas meaning not able to be cut. Democritus believed that there were sharp atoms and smooth atoms for different types of objects. -
Period: Jan 1, 1301 to Jan 1, 1500
Alchemists
Alchemists were the first to use the term element when talking about chemicals. Alchemy only focused on three elements though: mercury, salt, and sulfur. Alchemy restarted the fire of atomic theory by them trying to understand it as well. -
Antoine Lavoisier
Antoine Lavoisier was teh first scientist to discover that mass could neither be created or destroyed. He did this through conducting many different experiments. -
Benjamin Franklin
Benjamin Franklin discovered electricity. Furthermore, he discovered that electricity was made of positive and negative charges. John Dalton later added on to this by discovering that atoms had positive and negative charges as well. -
Joseph Proust
Joseph Proust discovered the Law of Definite Proportions which states that the ratio of elements in any compound is always going to be the same regardless of where it is from. For example, water from the ocean has the same composition as water from a hose. -
John Dalton
John Dalton was the first scientist to actually propose an atomic theory with spherical atoms. Dalton proposed that all matter was made of atoms along with three other principles that are not very far from modern atomic theory. -
Michael Faraday
Michael Faraday had some rather major impacts on modern atomic theory by relating electrons and protons to electricity. He added that matter must have positive and negative charges and that opposite charges attract while like charges repel. -
Henri Becquerel
Herni Becquerel was the first to discover radioactivity. This led to the discovery of alpha, beta, and gamma radiation. Ultimately, Becquerel's discoveries impacted quantum theory as well. -
Dmitri Mendeleev
Dmitri Mendeleev discovered and grouped the elements into 7 different groups. Within each group, there were similar properties, Mendeleev used these properties to determine which element belonged in which group. This became known as Periodic Law. -
William Crookes
William Crookes was accredited with the discovery of certain properties of cathode rays. He discovered that the raysare deflected by electric fields and magnets, travel in straight lines from the cathode to the anode, and they cause glass to glow. -
JJ Thomson
JJ Thomson developed the "plum pudding" model of the atom. This model included free floating electrons surrounded by positively charged matter. Ultimately, this model was disproven by many other scientists, but his impact was still great with finding the charge to mass ration of an electron. -
Ernest Rutherford
Ernest Rutherford's impact on the Atomic Theory was very great. His discovery of alpha, beta, and gamma radiation that was emitted from uranium and thorium eventually led to even greater developments in atomic theory and in technology as well. He also proposed a new model of the atom with the electrons being in a fixed orbit. -
Marie and Pierre Curie
Marie and her husband Pierre Curie both studied uranium and thorium and the decay of each. Ultimately, they deemed the decay processes radioactivity. In addition, they discovered polonium and radium. -
Max Planck
Max Planck discovered Blackbody Radiation in 1909. Blackbody Radiation is the emission of light from hot objects. He also concluded that energy can only be absorbed or released from atoms in certain amounts called quanta. -
Albert Einstein
Albert Einstein had many great contributions to the atomic theory, but most notably concluded his most known equation that energy is equal to mass times the speed of light squared. He also discovered the dual nature of light as particles and as waves. -
Robert Millikan
Robert Millikan was the scientist who conducted the oil drop experiment. This experiment was used to determine the charge and mass of individual electrons. -
Niels Bohr
Niels Bohr developed one of the atomic structures that is still widely used. Bohr discovered that atoms have a central nucleus with neutrons and protons in it that is surrounded by multiple orbitals of valence electrons. He was the first to discover that electrons moved in orbitals. -
Louis de Broglie
Louis de Broglie discovered that electrons had a dual nature. They could either be particles or waves. His theories supported those of Albert Einstein as well. -
Werner Heisenberg
Werner Heisenberg was one scientist who revolutionized the ideas behind the atomic theory by discovering that one can never know the position and velocity of a particle at the same time, but rather one or the other. -
Erwin Schroedinger
Erwin Schroedinger was very influential in terms of the atomic theory by being the first scientist to introduce wave mechanics as a model of the atom given the dual nature of particles. In addition, Schroedinger viewed the electrons as in clouds rather than in orbitals or other such models. -
James Chadwick
James Chadwick was the first scientist to discover the neutron. Using the experiment shown in the picture, James Chadwick found a strange area of radiation that came from the original source of alpha particles. This eventually led to the discovery of the neutron.
