Dalton's Atomic Model Essay

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Introduction
The model of the atom has developed greatly from Dalton’s model, which suggested that, ‘matter is composed of small, indivisible (cannot be divided) objects’, to the most recent model developed by Chadwick that includes a nucleus, electrons, protons and neutrons. These developments have all been due to continual experimentation and observation of matter. Chadwick’s model is still being added to and new parts of atoms are found all the time. The development of modern technologies has assisted scientists in creating the most up to date model of the atom, which without the scientists Dalton, Thomson, Rutherford, Bohr and Chadwick’s models we would not have.

Dalton’s Atomic Model
John Dalton’s atomic model was the first to be developed
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At the time of Thomson’s discovery of electrons he was unaware that they were in these shells and Thomson proposed that atoms were,’ uniform spheres of positively charged matter in which electrons are embedded’. The discovery of electrons occurred when Thomson used a cathode ray, which is a sealed glass container with two electrodes that are separated by a vacuum. Voltage is then applied across the electrodes and cathode rays are created. Thomson, through this experiment, discovered that the rays weren’t just light, but negatively charged particles. Through much experimentation Joseph Thomson made the discovery that Hydrogen was actually not the smallest unit of matter, but these particle or electrons as we know them were. Thomson then suggested that these electrons were distributed in a sea of positively charged particles to explain the overall neutral charge of atoms. Thomson is the creator of the plumb pudding model, which explains atoms as a spherical structure with electrons and protons distributed evenly throughout it. Thomson made advancements on John Dalton’s model of the atom by discovering electrons, which is one of the key features of the model of the …show more content…
Rutherford discovered the nucleus through an experiment in which he shot helium nuclei at a thin layer of gold atoms. Rutherford conducted this experiment believing that if Thomson’s model was correct the helium nuclei were unlikely to be deflected because the mass of an atom was spread evenly round it. Rutherford’s experiment was called the ‘gold foil’ experiment and through this he discovered that the helium nuclei were being deflected in almost the exact direction they came from. This experiment disproved Thomson’s plum pudding model, and Rutherford explained that the only way deflection of the nuclei was possible was if the positively charged particles were only in the nucleus. The ‘gold foil’ experiment lead to the adjustment of the plum pudding model to fit the results observed by Rutherford, and the creation of the planetary model of the atom. The model was quite different to Dalton and Thomson’s models as it showed protons clustered together in the centre of the atom surrounded by electrons in shells or rings. The model improved on the earlier models of the atom and is much closer to the model of the atom we know and use today, it shows a central nucleus with positively charged protons inside and shells surrounding it that contain negatively charged

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