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360
Aristotle's Atom (360 BC)
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410
Democritus Atom
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470
Democritus (circa 470 BC)
Democritus said that all matter is made up of tiny, indivisible particles called atoms. These atoms were completely solid and were eternally in motion. He also stated that every different type of atom differs slightly.
Democritus was admired by Aristotle. -
Antoine Lavoisier
Antoine Lavoisier formulated the theory of conservation of mass. This showed that matter (atoms) couldn’t be created or destroyed, which supported the theory of Democritus. Lavoisier also showed that compounds are simply combinations of different types of atoms, further supporting the idea that atoms are indivisible.
Date Adopted: late 18th century
Lavoisier provided crucial information for John Dalton’s model. -
John Dalton
Dalton compounded all the work of Lavoisier and Democritus into one, single atomic theory. This theory stated that all matter is made of indivisible and indestructible atoms, all atoms of a given element are identical, compounds are combinations of elements (atoms), and a chemical reaction is merely a rearrangement of atoms.
Date Adopted: 1803
Dalton built off the works of Lavoisier and Democritus. -
Dalton Atom
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Henri Becquerel
Henri Becquerel discovered radioactivity in his research of uranium and other materials. This helped to show what happened when atoms were affected and observed.
Date Adopted: 1896
Becquerel shared a Nobel Prize with the Curies. -
J.J. Thomson
J.J. Thomson conducted an experiment with a cathode ray tube, and bent the path of the rays with magnets. He interpreted this as evidence of much smaller particles, which he called electrons. Using this, he formulated the plum pudding model, which added negatively charged electrons into the positively charged solid part of the atom.
Date Adopted: 1898
Thomson was the teacher of Ernest Rutherford. -
Max Planck
Name: Max Planck created the quantum theory, which was later used by Niels Bohr to create his model of the atom.
Date Adopted: 1900 -
Marie and Pierre Curie
Name: Marie and Pierre Curie enhanced the understanding of radioactivity through their research of radioactive materials (discovering radium and polonium). This helped to show what happened when atoms were affected and observed.
Date Adopted: 1898
The Curies shared a Nobel Prize with Henri Becquerel. -
Robert Millikan
Robert Millikan discovered the exact charge of the electron in his “Oil Drop Experiment”, further enhancing the model of J.J. Thomson.
He performed this experiment with the aid of Harvey Fletcher.Date Adopted: 1908
He performed this experiment with the aid of Harvey Fletcher. -
Ernest Rutherford
Name: Ernest Rutherford performed an experiment where he shot alpha particles at gold foil, expecting them to pass right through. Some bounced back, however, and he formulated the planetary model, which showed that most of the mass of an atom was concentrated in the center (nucleus).
Date Adopted: 1909
Ernest Rutherford was the student of J.J. Thomson (he was trying to prove Thomson’s model with his experiment, but ended up disproving it). -
Niels Bohr
Niels Bohr said that electrons had quantified amounts of energy using Planck’s Quantum theory. He proposed a new model of the atom where the electrons travel around the nucleus in orbits determined by their energy levels.
Date Adopted: 1913
Consulted and looked up to Ernest Rutherford. -
Erwin Schrodinger
Name: Erwin Schrodinger introduced the Schrodinger equation, which allowed the motion of the electron to be determined more accurately. This increased the accuracy of Bohr’s model.
Date Adopted: 1926
Schrodinger succeeded Max Planck at the Friedrich Wilhelm University. -
Henry Mosely
Henry Moseley is best known for formulation Moseley’s Law. This law states that there is a systematic relationship between the energy (wavelength in x-ray spectroscopy) of a given element and its atomic number. This supported the periodic table and Bohr’s model of quantized energy.
Date Adopted: 1915 -
James Chadwick
Name: James Chadwick discovered the neutrally charged neutron, the discovery that ultimately led to the atomic bomb. He enhanced Bohr’s model by adding neutrons to the nucleus.
Date Adopted: 1931
Chadwick studied under Rutherford at Manchester College and Cambridge. -
Plum Pudding Atom (Thomson)
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Werner Heisenberg
Name: Werner Heisenberg created the uncertainty principle, which took away the accuracy of Bohr’s model (the new electron cloud model was proposed after this). He kept the idea of quantized energy in electrons, but took away the ability to predict where they will be.
Date Adopted: 1927
Heisenberg looked up to Max Planck as a mentor. -
Planetary Atom (Rutherford)
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Bohr Atom
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Electron Cloud Atom (Heisenberg)
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Period: to
A Few Important Notes
- If the date of a particular event starts with January 1st, the exact one in unknown (just take the year into account).
- The scientists are listed by their birthdate, and the date their work was accepted is in the description.
- If the scientist proposed a new model of the atom, it is listed as a separate event.
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Aristotle (384 BC)
Aristotle said that atoms were composed of the four elements: fire, water, earth, and air. Each of these atoms had certain properties depending on what they were made of: hotness, dryness, wetness, or coldness. This contradicted the work of Democritus and put a second theory in use for almost 2000 years (before it was disproved). He also originated a method of gathering scientific facts and recording them methodically. Aristotle admired Democritus as a role model.
