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340
Aristotle
Aristotle did not think taht atoms could be constantly moving if they were in a void. He believed that there were four elements and four qualities and that they would align into their rightful place and be at rest. -
460
Democritus
In Greece, 460 BC, Democritus formulated an atomic theory similar to modern science's understanding of the atom. This theory suggested that atoms can't be destroyed and that they only differ in shape, position and arrangement. -
Robert Boyle
In 1650, Robert Boyle measured relationships between volume and pressure of gasses. From his experiments, he was able to conclude that gasses are made up of tiny particles that group together to make different substances. -
Issac Newton
In England, 1704, Issac Newton formulated a theory of loght, the three laws of motion, and even suggested a mechanical universe with small, solid masses in motion. In relation to the atomic theory, Newton suggested that atoms are held together with attractions, otherwise known as forces. He also stated that "matter is formed of solid, massy impenetrable particles”. -
John Dalton
In England, 1803, he proposed an atomic theory that stated all mattter is composed of small indivisible particels termed atoms. Atoms of a given element possess unique characteristics and weight. He also stated that three types of atoms exist: simple, otherwise known as elements, compunds, or simple molecules, and complex, or complex molecules. -
George Johnstone Stoney
In Ireland, 1894, George Johnstone Stoney introduced the term electron and estimated the charge carried by a single hydrogen atom. This lead to the introduction of the term "fundamental unit quantity of electricity. -
Joseph John Thomson
In England, 1897, Joseph John Thomson discovered the electron and isotope. He also invented the mass spectrometer. This led to the Nernst-Thomson rule which explains that it is difficult for charged ions to attract each other through insulating water molecules, in order for them to dissociate. -
Max Planck
In Germany, 1900, Max Planck theorized that " A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die and a new generation grows up that is familiar with it. This led to his title as the Founder of the Quantum Theory. -
Hantaro Nagaoka
In Japan, 1903, Hantaro Nagaoka created an early model of an atom using an analogy based on Saturn's rings. He also worked with British physicist C.G. Knott on spectroscopy. -
Robert Andrews Millikan
In America, 1909, Robert Andrews Millikan used an oil drop exxperiment to measure the charge of an electron. -
Ernest Rutherford
In both Britain, and New Zealand in 1911, Ernest Rutherford discovered the concept of the radioactive half life. He also differentiated an named alpha and beta radiation. Rutherford is credited for performing the first splitting of an atom. -
Henry Moseley
In England, 1914, Henry Moseley contributed to our understanding of the atom by measuring the wavelengths of the x-rays given off by certain metals. Moseley was bale to determine the number of positive charges in the nucleus of an atom. This was the first concept of the atomic number. -
Neils Bohr
In Denmark, 1922, Neils Bohr expanded on Rutherford's earlier theory. Bohr published his theory which suggested that electrons travel in specific orbits around the nucleus, and that outer orbits can hold more electrons than the inner orbits and that these orbits determine the chemcial properties of the atom. -
James Chadwick
In England, 1932, James Chadwick discovered the neutron, named because of its lack of electrical charge, which was previously an unknown particle in the nucleus of an atom.
