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460 BCE
Democritus
Democritus was a central figure in the development of the atomic theory of the universe. He theorized that all material bodies are made up of indivisibly small atoms. Democritus was born into a noble family in the Ancient Greek city of Abdera. -
427 BCE
Plato
Plato theorized that solid forms of matter are composed of indivisible elements shaped like triangles. This was contrary to the thought that atoms were shaped like spheres. -
760
The Alchemists
The Alchemists were chemistry practicioners that became known as chemists. They observed that substances continuously changed from one form to another, which helped add to the Atomic Theory. -
Robert Boyle
Robert Boyle formed the Experimental Philosophy club at Oxford, and also created Boyle's law, which showed the inverse relationship that exists between the pressures and volumes of a gas. -
Antone Lavoisier
Antone was a French chemist and leading figure of the 18th century. -
John Dalton
John Dalton's most influential work in chemistry was his work on the Atomic Theory. He based his theory off of partial pressures on the idea that only like atoms in a mix of gases repel each other, unlike how atoms appear to react indifferently towards each other. -
Billiard Ball Model
John Dalton defined an atom to be a ball-like structure, as the concepts of atomic nucleus and electrons were unknown at the time. -
Amadeo Avogadro
Amadeo stated that equal volumes of gases at the same temperature and pressure contain the same number of molecules regardless of their chemical nature and physical properties. Amadeo was an Italian Mathematical Physicist. -
Dmitri Mendeleev
Dmitri devised the periodic classification of the chemical elements so that they were arranged in order of atomic weight. Dmitri was a Russian Chemist. -
J.J. Thomson
J.J. Thompson experimented with cathode ray tubes. Through this, J.J. proved that all atoms contain tiny negatively charged subatomic particles. Thomas began studying at Owens College at the age of 14! -
Pierre and Marie Curie
Pierre and Marie discovered strongly radioactive elements, polonium and radium, which helped to add to the atomic theory. Marie coined the term radioactivity by the spontaneous emission of ionizing. -
Albert Einstein
Albert Einstein proved mathematically the existence of atoms, which helped revolutionize all sciences through the use of statistics and probability. He became famous for the theory of relativity. -
Robert Millikan
Robert Millikan succeeded in determining the magnitude of the electron's charge. This added to the atomic theory. Robert was also honored with the Nobel Prize for Physics in 1923. -
Ernest Rutherford
Ernest Rutherford established that the mass of the atom is concentrated in its nucleus. Ernest was born in New Zealand. -
Niels Bohr
Neils Bohr received the Nobel Prize in physics in 1922. He developed the Bohr model of the atom, and made the principle of complementarity, showing that things could be seperately analyzed in terms of contradictory phases. -
Henry G.J. Mosely
Mosely created Mosely's Law, which states that the square root of the frequency of the X-ray emitted by an atom is proportional to its atomic number. Mosely was also an English Physicist. -
Solar System Model
The main idea of the solar system was proposed by the Polish astronomer Nicolaus Copernicus, and was later made into forms of Solar System Models. -
Electron Cloud Model
Thanks to this model, electrons were no longer shown as particles moving around a central nucleus in a fixed orbit. Instead, it was proposed as a model where scientists could only make educated guesses as to the positions of electrons and as to where the electrons are likely to be found. -
James Chadwick
James Chadwick discovered the neutron. Ernest Rutherford had earlier proposed that such a particle might exist in an atomic nucleus. This now proven, it was called a neutron. James was awarded the Nobel Prize for Physics in 1935.