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Democritus
He found that:
1. All matter consists of invisible particles called atoms.
2. Atoms are indestructible.
3. Atoms are solid but invisible.
4. Atoms are homogenous.
5. Atoms differ in size, shape, mass, position, and arrangement.
->Solids are made of small, pointy atoms.
->Liquids are made of large, round atoms.
->Oils are made of very fine, small atoms that can easily slip past each other. -
John Dalton
John Dalton developed an atomic theory in the 1800s. He did experiments, his most important conclusions are summarised below
All matter is made of atoms Atoms cannot be broken down into anything simpler.
All the atoms of a particular element are identical to each other.
Atoms are rearranged in a chemical reaction.
Compounds are formed when two or more different kinds of atoms join together -
J.J Thompson
JJ Thompson discovered the electron in 1897. This showed that the atom contained smaller pieces, whereas Dalton had thought that atoms could not be broken down into anything simpler. -
Ernest Rutherford
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Marie & Pierre Curie
They announced the discovery of radium and polonium in 1898 -
Max Planck
Used the idea of quanta (discrete units of energy) to explain hot glowing matter. -
Albert Einstein
He invented a mathematical method of calculating the size of atoms and molecules in early 1905. -
Ernest Rutherford
In 1911 Ernest Rutherford used experimental evidence to show that an atom must contain a central nucleus. This was further evidence that an atom contained smaller pieces. -
Neils Bohr
Niels Bohr further developed Rutherford's nuclear atom model. He used experimental evidence to support the idea that electrons occupy particular orbits or shells around the nucleus of an atom. -
James Chadwick
Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron in 1932.
