Fundamental Particles

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History of the Atom

Greek philosophers - matter made up of a single continuous substance that produced the four elements (fire, earth, water and air).

Democritus - first to suggest the existence of atoms. He called them atomos. Atoms are tiny, indestructible and indivisible.

Alchemists - built up evidence about how substances behave and combine. Their aim was to change other metals into gold.

1661 Robert Boyle - proposed there were some substances that could not be made simpler. (the chemical elements).

1803 John Dalton - Elements were composed of indivisible atoms. All atoms of a particular element have the same mass. Atoms of different elements had different masses. Atoms could not be broken down.

1896 Henri Becquerel - Discovered radioactivity. Showed that particles could come from inside the atom.  Therefore atom was not indivisible. 

1897 JJ Thomson - Discovered the electron. The first sub-atomic particle to be discovered. Thomson showed electrons were negatively charges and electrons were the same for all elements. 

As electrons had negative charge and were much lighter than the atom, a positive charge had to cancel out the negative charge and…

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