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100
Thales
•Born in 620 BC in Greece and dies in 546 BC.
•Believed that all matter originally came from water.
•Discovered that after rubbing a piece of amber with fur, it would attract light objects to it.
•He suggested that this force came from the amber, although he didn’t make the connection with any atomic particle or electricity. -
260
Democritus
•Born 460 BC in Greece and died 370 BC.
•Wondered if matter could always be divided into smaller pieces, or if there was limit to the amount of times it could be divided.
•Discovered that matter couldn’t be divided into smaller pieces forever, that there was a limit to how small it could go.
•Named the smallest piece of matter “atomis”.
•He thought that atoms were small, hard particles, all made from the same things, although being different shapes and sizes, and there was an infinite amount. -
336
Aristotle
•Born in 384 BC in Greece and died in 322 BC
•Believed in four elements – air, water, earth, fire
•Thought that you could keep cutting matter regardless of how small it is.
•His theory was believed for approx. 2000 years, mainly because he was the tutor to Alexander the Great. -
Antoine Lavoisier
•Born in 1743 in France and died in 1794.
•Discovered that water is made from hydrogen and oxygen.
•Performed an experiment where he burned graphite and diamonds to both produce carbon dioxide.
•Invented the analytical balance.
•Proved that chemical elements weren’t created or destroyed, but were combined in chemical reactions.
•John Dalton used Lavoisier’s work to help create his own atomic theory. -
John Dalton
•Born in Cumberland England and died 1844.
•Explained the behaviour of atoms in terms of weight.
perimented with/examined gases.
•Looked at it in meteorology terms.
•Found that air wasn’t a chemical solvent, but a mechanical system.
•Atomic theory - All matter is made from atoms. They cannot be destructed or divided. All atoms in an element are the same mass. Compounds are two or more different kinds of atoms combined. A chemical reaction is a group of atoms rearranging. Atoms can't be created. -
Michael Faraday
•Born in 1791 in England and died in 1867.
•His law implied that both matter and electricity were made from atoms, although he was strongly against the idea of atoms, especially Dalton’s theory.
•He believed that matter was where lines of force met in a particular spot.
•During experiments he did trying to prove his theory, he discovered the magneto-optical effect and diamagnetism.
•Faraday’s theory was not accepted for quite a while because most physicists saw it as nonmathematical. -
Dmitri Mendeleev
•Born in 1834 in Siberia (Russia) and died in 1907.
•Maker of the periodic table•Arranged elements (2 or more atoms joined together) into 7 different groups.
•The elements were put in ascending order by their atomic weight.
•He left gaps in the table for elements that had not yet been discovered. -
Joseph Thomson
•Born in 1856 in Britain and died in 1940.
•His theory is known as the “plum pudding model”.
•Before Thomson’s theory, it was believed an atom was like a small solid ball.
•He discovered electrons, and suggested that the atom could be divided into smaller pieces, protons and electrons.
•He thought that an atom had a sphere of positive charge with negative electrons inside it. They would balance each other out, making the atom neutral. -
Ernest Rutherford
•Born 1871 in New Zealand and died 1937
•Did an experiment with two scientists about the deflection angles of alpha particles, by shooting them through a very thin piece of gold.
•Discovered that the atom has most of its mass in the centre of it, in a nucleus, with the rest of the atom mostly being empty space.
•The nucleus only took up one-billionth of the mass of the entire atom. Even smaller particles, electrons, orbit around the nucleus.
•Is now known as the planetary model. -
Niels Bohr
•Born in 1885 in Denmark and died in 1962.
•Proposed a shell model to explain that electrons could have stable orbits around the nucleus.
•He changed Rutherford’s model by suggesting that the electrons orbit the nucleus without losing their energy, meaning that low energy electrons would orbit closer to the nucleus than electrons with higher energy. -
Erwin Schrodinger
•Born in 1887 in Austria and died in 1961.
•Looked at Bohr’s atomic theory and improved it.
•He used mathematical equations to describe the chances of finding an electron in a particular area. This is known as the quantum mechanical model.
•It doesn’t describe the exact path of an electron like Bohr’s, but predicts the odds of the location of an electron. -
James Chadwick
•Born 1891 in England and died 1975.
•Discovered the neutron, the particle Rutherford had thought of as having a lot of mass with no charge.
•Three subatomic particles had now been identified (protons, electrons and neutrons).
•This helped to explain observations made, such as the existence of radioactive differences in the same element.
•Chadwick was able to explain isotopes, things of the same element which have the same number of protons and electrons, but with different amounts of neutrons. -
Louis de Broglie
•Born in 1892 in France and died in 1987.
•At the time it was believed that wave and particles interpretations of light and matter were different to each other.
•He suggested that they were in fact the same, just viewed from different perspectives.
•This theory helped to explain how atoms, molecules and protons behaved, and was inspired by Erwin Schrödinger. -
Werner Heisenberg
•Born in 1901 in Germany and died in 1976
•Looked at Bohr’s and de Broglie’s theories, and determined that it isn’t possible to measure the exact position and velocity of an electron at the same time
•If you wanted to find the position of an electron to great accuracy, you would not be able to tell the velocity of it, and vice versa.
•The uncertainty isn’t because of an imperfection in the technique, but is just the nature of matter. -
Paul Dirac
•Born in 1902 in Britain and died in 1984.
•Founded the field of quantum physics.
•Developed a mathematical formula that incorporated both Heisenberg’s and Schrödinger’s theories.
•Discovered what is now known as the Dirac equation, an equation describing electrons.
•This led him to find the existence of the positron, the antiparticle of the electron.
