Empedocles, a Greek philosopher proposed that there were four fundamental substances: EARTH, WIND, FIRE and WATER.
Democritus’s atomic theory stated that all matter is made up of small units called atoms which cannot be destroyed. Democritius’ model is the earliest of the atomic model’s written down. He was the first to use the term “atom.” However, Democritius thought that atoms were combined in a hook and eye system but we now know today that this is not true.
Aristotle’s theory was that all matter was made of the four elements/ fundamental substances stated by Empedocles (fire, water, earth and wind). He also believed that there were four qualities to these elements; dryness, hotness, coldness and moisture.
John Dalton’s atomic theory stated that elements consist of tiny particles called atoms and that all the atoms of elements have identical properties. He also stated that compounds are elements which are joined together. He proposed a system of symbols to represent atoms of different elements.
Dimitri Mendeleev created the periodic table. His table was arranged according in ascending order of atomic weight and he also left spaces for the elements that were yet to be discovered.
J.J Thompson calculated that mass to charge ratio. He also deduced that the electron was part of matter. He also introduced the Plum Pudding structure – a positive sphere with embedded (negative) electrons
Phillip Lenard put together a revised atomic model stating that each atom has positive and negative particles joined together. He also did a lot of work with electrons and received a Noble Peace Prize for it.
Ernst Ruerford revised and corrected Phillip Lenard’s theory. He stated that instead of having the positive and negative particles joined together, the nucleus is positively charged and in the middle of the atom and the rest of the atom was empty with the elethctrons orbiting around it. However, in 1919 he discovered protons and the fact that they were positively charged.
Neils Bohr added to the atomic model that the outer shells of electrons could hold more electrons than the inner ones. Neils Bohr’s model is very similar to the modern atomic model
The Modern Atomic model states that the middle of atom is made up of the nucleus where protons and neutrons reside. The electrons orbit around the nucleus in shells, the outer shells being capable of holding more electrons than the inner ones. The electrons orbit in a plant- like way being that they don’t go symmetrically around the nucleus but rather take distorted paths.