The History of Atomic Theory. Due to the constantly developing scientific theories, the model of the atom has changed significantly over the years from Democritus with his views of indivisible tomos to Thomsons plum pudding model and scientists

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History of Atomic Theory

Due to the constantly developing scientific theories, the model of the atom has changed significantly over the years – from Democritus with his views of indivisible átomos to Thomson’s plum pudding model and scientists’ most recent proposition: quarks.

During the 5th Century BC, the first idea of the atom was devised. The Greek philosopher, Democritus, came up with his theory on the atom. He suggested that each of the four elements (earth, air, fire and water) consisted of atoms which were held together by miniscule hooks. Another of his beliefs was that a sample of matter could not be divided an infinite number of times - everything was made of a base particle which he termed ‘átomos.’

At the beginning of the 19th century, John Dalton came up with his own theories on the atom.  He predicted that atoms made up elements and that they could not be divided, agreeing with Democritus. He also believed that all atoms of a given element were the same, and that atoms of one element were different to those of any other element. However, by then the number of elements had grown from 4 and included substances such as ‘potash,’ ‘soda’ and ‘lime,’ with none of the Greeks’ elements remaining.

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During experiments with cathode rays around the turn of the 20th century, JJ Thomson discovered the electron. He realised that these cathode rays were a stream of particles and that they all had negative charges and small masses. They could also be deflected by electrical fields and magnets and Thomson concluded that the atom was further divisible, disproving the theory of Dalton and the Greeks. He decided that electrons came from within the atoms – his theory being that an atom was made up of electrons floating in a ‘sea’ of positive charge, with the atom’s overall charge being neutral. ...

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This essay is well written, there are no issues with spelling or grammar, the essay is coherent and the information links together, making it easy to read. To add to this the candidate clearly shows an understanding of the scientific theories mentioned.

Unfortunately the candidate fails to discuss modern theories relating to the atom which include the theories of quantum mechanics and the quark model. As the protons and neutrons that make up an atom are themselves made of up different quarks, this is an essential piece of information when discussing the development of our understanding of the atom. By not discussing this the candidate demonstrates a lack of understanding of current ideas. However on a more positive note the candidate has clearly undergone independent research to discuses the development of the atom, this is shown by the inclusion of names and dates relating to the development of the different theories. As well as this they have included several images, which help to explain the theories mentioned. Though I would advise that you write a bibliography stating any sources you use to help write your essay, this includes images, it is also a good idea to give links to webpages used. Finally the conclusion could be improved by summarising the main ideas relating the different atomic models and stating why each is important, this helps draw the essay to a close.

The candidate's introduction starts off well but they fail to state what they plan to cover in this essay, which is an essential part of a good introduction. However the candidate gives a good description of the different theories of the atom and the information provided is informative and interesting to read.