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A greek scholar named Empedocles proposed matter was composed of 4 elements. ie earth, air, fire and water. He checked some theories experimentally by proving that even though air was invisible it still took up space, ie proving it is matter. -
Democritus (greek scholar) suggested that matter was made of tiny particles that could not be broken down further.
- He called the particles atoms after the greek word atomos
- This was a new concept from Empedocles' thoughts on the elements.
- This concept never took off due to Socrates not believing in this theory. -
Aristotle (Philosopher) believed in Empedocles theory of the four element model despite the new atomic model proposed by Democritus. Aristotle was a very renowned philosopher. Thus, this helped the four element model be accepted for 2000 years. -
Many alchemists of this era believed that metals grew the same way that plants would. Thus, they attempted to turn cheap metals such as iron or lead, into gold. They created chemical symbols, that we now recognize as compounds and elements. Also, they created laboratory materials that we still use today, such as beakers, filters, stirring rods and more. The belief on matter stayed the same as alchemists believed in the "four element" model in these times.
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Robert Boyle (English Scientist), didn't believe in the "four element" model. Robert Boyle also redefined the word element into the way we know it today, a pure substance that cannot be chemically broken down into simpler substances. Furthermore, Boyle believed air was a mixture rather than an element. No other changes were made to the "four-element" model. -
Josh Priestly was the first to isolate oxygen, but he didn't realize that oxygen was an element. However, Antoine Lavoisier concluded that air must be a mixture of two or more elements. Oxygen was one of them. Meanwhile, Henry Cavendish mixed metal with acid. He accidentally created a flammable gas lighter than air, it wasn't known that this gas was hydrogen. But, he discovered this gas would fuse with Priestly's oxygen, making water. People believed that water was an element at the time. -
By this time, the two previous theories had been merged together. John Dalton (English Chemist) published a theory of why elements differ from each other and from other non-elements. Dalton's atomic model stated that all matter is made of atoms, each element has its own kind of atom, compounds are created when two atoms of different elements form a molecule and atoms cannot be created nor destroyed. This theory was really a further explanation of Democritus' model from 2000 years in the past. -
Michael Faraday discovered that electric current would cause chemical changes in some compounds in solution. The atoms could gain electric charges and form atoms called ions. Michael Faraday further added on Dalton's atomic model, matter must contain positive and negative charges, opposite charges attract and matching charges repel, atoms form molecules due to the electric charges in between them. -
J.J. Thomson revised the atomic model further. He discovered very light negative particles known as electrons. He also experimented with beams of much heavier positive particles, these particles are known now as protons. J.J. Thomson's new model was known as the "raisin bun model" and it consisted of rules, such as how atoms contain electrons, electrons are light and have a negative charge, the rest of the atom has a positive charge and the resulting atoms are neutral or uncharged. -
The japanese scientist Hantaro Nagaoka who was working at the same time, showed the atom as a large positive sphere surrounded by a ring of negative electrons. -
A man working at McGill university known as Ernest Rutherford designed an experiment to test Thomson's and Nagaoka's raisin bun theory. He aimed a type of radiation called alpha particles (positively charged particles smaller than most atoms) at a thin sheet of gold foil. He guessed that the particles would pass straight through the gold foil, most of them did. A tiny number of the alpha particles bounced back from the gold foil. To this explain this phenomena, he created the nuclear model. -
The nuclear model contains a few properties, an atom has a tiny, dense, positive core called the nucleus (which deflected the alpha particles and contains protons). The nucleus is surrounded mostly by empty space, containing rapidly moving negative electrons (through which the alpha particles passed unhindered). This is very similar to what we believe today and this further explained the raisin bun model because it demonstrated how atoms resemble.