history of the atom Flashcards
when was the electron discovered and what is it
At the end of the 1800s, a scientist called Thomas Dalton discovered the electron. This is a tiny, negatively charged particle
how did Thomas discover the electron
Thomson was experimenting by applying high voltages to gases at low pressure
what did Thomas say about his version of the atom
He said that the tiny negatively charged electrons must be embedded in a cloud of positive charge.
what did Thomas call his version of the atom
Thomas called his version of the atom the plum pudding model which was a sphere of positive charge with electrons in it
what experiment did Geiger and Marsden do
Geiger and Marsden were doing an experiment with radioactive particles. They were firing dense, positively charged particles (called alpha particles) at the thinnest piece of gold foil they could make. They expected the particles to pass straight through the gold atoms with their diffuse cloud of positive charge. this changed the plum pudding theory
what did Rutherford suggest about Thomases atomic model
Rutherford suggested that Thomson’s atomic model was not possible. as the positive charge must be concentrated at a tiny spot in the centre of the atom.Otherwise the large, positive particles fired at the foil could never be repelled back towards their source.
what was Rutherfords version of the atom
Rutherfords version of the atom was a positively charged nucleus surrounded by atoms
when was the next important development of the atom
The next important development came in 1914, when Niels Bohr revised the atomic model again.
what did Niels Bohr notice and suggest about the atom
He noticed that the light given out when atoms were heated only had specific amounts of energy. He suggested that the electrons must be orbiting the nucleus at set distances, in certain fixed energy levels.
what is a neutron
a neutron is a sub-atomic particle in the nucleus.
what charge is the neutron
neutrons have no charge and has the same mass as a proton
