2. The history of the atom

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In this episode, Dr Sunayana Bhargava and Tulela Pea explore the history of the atomic model, and how that has developed over the past two centuries. Suitable for: AQA, Edexcel, OCR. For more information on the history of the atom, check out the BBC Bitesize website: https://www.bbc.co.uk/bitesize/guides/zwn8b82/revision/1 Key learning objectives discussed in this episode include: - Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided. - The discovery of the electron led to the plum pudding model of the atom. The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it. - The results from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged. This nuclear model replaced the plum pudding model. - Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances. The theoretical calculations of Bohr agreed with experimental observations. - Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, called protons. - The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus. This was about 20 years after the nucleus became an accepted scientific idea.