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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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Introduction

Chemistry Assignment 1v2                

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.

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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.’

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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.

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Middle

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This model was short-lived, however. In 1909, work began that led to the downfall of the ‘plum-pudding’ model. Hans Geiger and Ernest Marsden, two of Ernest Rutherford’s students, were carrying out a series of experiments at the University of Manchester. Some α (alpha) particles were directed at a sheet of gold foil and measured the particles’ deflection. Rutherford predicted that the α particles would not be deflected by Thomson’s plum pudding model.

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However, as shown in the above diagram, whilst most particles were not deflected, the centremost particles were. This indicated that there was a small, concentrated positive charge in the centre of the atom. In 1911, he proposed the nuclear atom. He said that the positive charge and most of the atom’s mass is concentrated in the centre, in a nucleus. Between the orbiting electrons and the nucleus would be most of the atom’s volume. Finally, the overall charge must be neutral.

In 1913, Niels Bohr modified Rutherford’s model slightly to change the electrons’ orbital paths.

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Conclusion

x, py, pz), the d level holds five orbitals (dz2, dxz, dyz, dxy, dx2-y2) and the f level holds seven. Instead of electronic configuration being shown as ‘shell 1, shell 2, shell 3 etc,’ they are shown as a list of orbital arrangements: for example, Oxygen is shown as 1s2 2s2 2p4.

Neutrons were finally discovered in 1932 by Englishman James Chadwick. He used high energy α particles to bombard lighter elements and found that a new form of radiation was emitted. This radiation was made up of particles with the same mass as a proton but had no charge. Different elements have different isotopes; meaning that they have a different number of neutrons – for the periodic table, the weighted average of known isotopes is taken.

Scientists are continuously working on creating new theories and strengthening old ones. Chemistry is constantly evolving and the model of the atom is still changing today as technology improves. Whilst it is true that science has come a long way since the four elements of the Greeks, it is likely that in the future the atom’s model will become even more complex.

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Response to the question

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 ...

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Response to the question

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.

Level of analysis

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.

Quality of writing

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.


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Reviewed by pictureperfect 03/07/2012

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