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5 Cards in this Set
- Front
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What did John Dalton do and in what year? |
In the early 1800s, John Dalton our forward his ideas about atoms, he suggested that substances were made up of atoms that were like tiny, hard spheres. He also suggested that each chemical element has its own atoms that differed from others in their mass. He believed these couldn’t be divided or split In chemical reactions he suggested that atoms re-arranged themselves and combined with other atoms in new ways. His ideas are still useful today to help visualise elements, compounds and molecules, as well as solids, liquids and gases |
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What did JJThomson do and when? |
At the end of the 1800s JJ discovered the electron, Thomson was experimenting by applying high voltage to gases at low pressure, Thomson did this on the beams of particles . They were attracted to positive charge showing they must be negatively charged themselves. Thomson proposed a different model for the atom, he said the tiny negatively charged electrons must be embedded in a cloud of positive charge, he knew the atoms themselves carried no overall charge so any charges in an atom must be balanced out. He imagined the electrons as the bird of plum in a plum pudding |
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What did Geiger, Marsden and Rutherford find out and when? |
In 1900s Geiger and Marsden were firing dense positively charged particles (alpha particles) at the thinnest price of gold foil they could make. They expected the particles to pass straight through the gold atoms with their diffuse colour or positive charge ( like Thomson’s plum pudding model) but instead Rutherford suggested that Thomson’s atomic mode was not possible as the positive charge must be concentrated in a tiny spot on the centre of the atom otherwise the large positive particles fired at the foil could never be repelled backwards towards the source. It was proposed that the electrons must be orbiting around the nucleus which contains very dense positively charged protons |
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What did Neil’s Bohr find out and when? |
In 1914 Niels Bohr noticed that the light given out when atoms were heated only had specific amounts of energy. He suggested that the electrons must be orbiting around the nucleus as set distances, in certain fixed energy levels. Yes he energy must be given out when excited electrons fall from a high to low energy level. Bohr matched his model to the energy values observed |
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What did James Chadwick do and when? |
In 1932 James Chadwick did an experiment that could only be explained by the existence of neutrons. Scientists had evidence of protons but a second sub-atomic particle in the nucleus was proposed the explain the missing mass that had been noticed in atoms. These neutrons must have no charge and be the same mass as a proton |
