-
460
Democritus
Lived from 460 BC to 370 BC in Greece.Democritus did not carry out experiments, but proposed hypotheses based on thought and reasoning. -
Jul 4, 624
Thales
Lived from 624 BC to 546 BC in Greece.He proposed the idea that water was the origin and basis of all matter. Although this does not seem to be correct, there is some truth in it that helped the growth of the atomic model. Water is nessecary to life, and the first life forms came from the oceans, so scientists understood his ideas and used them to develop their own atomic theories. Thales's water based theory was not disproved until the 1700’s -
Isaac Newton
Lived 4th January 1643 to 31st March 1727 in England.Performed many experiments on the structure of light.Discovered that white light has the same system of colours that can be seen in a rainbow, as well as the behaviours of light.Newton understood that atoms or particles move. Proposed a mechanical universe with small, solid moving masses.Suggested that atoms are held together with forcesBelieved that matter is formed of solid, massy, indestructible particles. -
Antoine Lavoisier
Antoine Lavoisier lived August 26th 1743 to May 8th 1794 in France. He studied the composition of chemical compounds, discovering that compounds containing more than one element always had the same amount of each element. -
John Dalton
Lived 6 September 1766 to 27 July 1844 in EnglandThe structure of mixed gases; on the pressure of steam and other vapours at different temperatures, both in a vacuum and in air; on evaporation; and on the thermal expansion of gases. -
Robert Brown
Robert Brown lived December 21st 1773 to June 10th 1858 in Scotland and England. Botanist Robert Brown performed an experiment where pollen grains were put on water and observed, to find that the pollen grains constantly changed directions in random patterns as if bumping into something invisible. Brown discovered that the explanation to this was that the pollen was hitting particles of water - causing the movement. This movement has been named the Brownian motion, after Robert Brown. -
Aristotle
Lived from 15th February 1826 to 5th July 1911 in Ireland and England. Most famous for his theory that electricity was made of separate negatively charged particles he called electrons.He introduced electrons as the "fundamental unit quantity of electricity". He also made notable contributions to cosmic physics and the theory of gases, such as estimating the charge carried by a single hydrogen atom. -
George Johnstone Stoney
Lived from 15th February 1826 to 5th July 1911 in Ireland and England. Most famous for his theory that electricity was made of separate negatively charged particles he called electrons.He introduced electrons as the "fundamental unit quantity of electricity". He also made notable contributions to cosmic physics and the theory of gases, such as estimating the charge carried by a single hydrogen atom. -
Joseph John Thomson
Joseph Thomson lived from December 18th 1856 to August 30th 1940 in England.Thomson discovered that atoms actually were divisible, and made up of even smaller negatively charged particles, which we now know as electrons. This helped him to suggest that an atom is like a plum pudding – the positively charges material being the cake and the electrons being the fruit. This was named the Thomson plum pudding model. -
Hantaro Nagaoka
Hantaro Nakaoka lived from August 15th 1865 to December 11th 1950 in Japan. Nagaoka worked on spectroscopy and created an early but incorrect model of an atom using similarities to Saturn’s rings. He proposed the theories that: The nucleus was very massive (like a very massive planet), and electrons orbiting the nucleus were bound by electrostatic forces (like the rings orbiting Saturn, bound by gravitational forces). -
Robert Andrews Millikan
Lived March 22nd 1868 to December 19th 1953 in the United StatesMeasured the charge of the electron using an oil drop and worked on the photoelectric effect.Helped scientist to understand the atom and proved JJ Thomson’s hypothesis that the mass of an electron is at least 1000 x smaller than the smallest atom. -
Ernest Rutherford
Lived August 30th 1871 to October 19th 1937 in Britain. (New Zealand born).He is most famous for the gold foil experiment, which helped him to understand the interior of an atom. He discovered that there is a nucleus in the centre of an atom, as well as that an atom is mostly empty space with a large amount of positive charge.These discoveries lead to the model of the atom known as the Rutherford nuclear model. -
Henry Moseley
Lived from November 23rd 1887 to August 10th 1915 in England. Moseley developed the application of x-ray spectra to study the structure of an atom.He discovered that the number of protons in an element determines its atomic number. This was by measuring the wavelength of the x-rays given off by particular metals, and from that he could find the number of positive charges (protons) in the nucleus of an atom. This was the first concept of the atomic number. -
James Chadwick
Lived from October 20th 1891 to July 24th 1974 in England.Chadwick discovered neutrons (neutral particles with no electrical charge). He found they were different from alpha particles because they repelled electrical forces that are in the nucleus of many atoms. He proved that neutrons making up about half the mass of an atom existed. -
Niels Bohr
Bohr studied the structure of an atom. He suggested that electrons didn't spiral into the nucleus, but orbit in different levels. This is called the Bohr model, or the quantum model. The more energy an atom gives off, the closer it is to the nucleus, the more it absorbs, the farther away. Outer orbits can hold more electrons than the inner orbits and that these orbits determine the chemical properties of the atom
