Events
Empedocles 450 BC
Empedocles came up with the 4 elements model. His theory proposed that everything was made up of combinations of 4 elements which are Water, Earth, Fire and Air.
He tested his ideas experimentally and was able to show that air existed.Democritus 400 BC
Democritus theorized that matter is made up of tiny particles that can not be broken down smaller. He called these particles atoms. Different elements are made up of different atoms.
He tried simple experiments to test his theory.Aristotle 350 BC
Aristotle favoured the 4-element model and he generally influenced everyone so they did not believe elements were made of atoms. He did not believe that empty space existed. Aristotle wrote and spoke about his believes.Robert Boyle 1650
Boyle introduced a new definition of element as a substance that could not be broken down into simpler substances. He discovered that air is a mixture and not an element. Boyle tested his theory using experiments. He created an experiment to show that the pressure of a gas changed when its volume changed.John Dalton 1808
Dalton created an atomic model theory to explain why elements differ from each other. His theory stated that:
- Matter is made up of atoms.
- Each element has its own kind of atom, along with its own particular mass.
- Compounds are created when atoms of different elements are joined together.
- Atoms cannot be created, destroyed or subdivided in chemical changes.
He performed experiments and tested the results. Dalton performed experiments to test his theory.Micheal Faraday 1831
Faraday discovered that atoms have an electrical charge component. This altered Dalton's atomic model because Faraday did not believe atoms were indestructible. He believed that:
- Matter contains positive and negative charges.
- Opposite charges attract each other and the same charges repel each other.
- Atoms can bind to form compounds because of electrical attractions between atoms.
Faraday performed experiments to test his theory.J.J Tompson 1904
Thomson discovered electrons and protons while experimenting with cathode rays. He showed that cathode rays were negatively charged. These cathode rays were elections. This discovery deprived Dalton's atomic model.Ernest Rutherford 1911
Rutherford created a nuclear model theory. He performed an experiment to test Tompson’s model and created his theory based on the test results. Rutherford's nuclear model theory stated that:
- Atoms have small centers with positive charge surrounded by negative-charged electrons.
- Atoms are made up of mostly empty space.Periods
Alchemists 500 - 1600 AD
The Alchemists came up with chemical symbols for elements and compounds.
They tried to change a substance from one kind to another. While experimenting they invented laboratory equipment to help them.Joseph Priestley/Antoine lavoisier late 1700s
Priestley was the first person to isolated oxygen scientifically. Antione Lavoisier experimented with oxygen and reacted it with inflammable air which is hydrogen to produce water. He concluded that air is a mixture containing oxygen.
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