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Democritus thinks of the atom
He thought that if you kept cutting a piece of silver in half you would end up with an invisible particle called an atom. He said atoms are small, hard particles made of one material that can be formed into different shapes and sizes. He also said that atoms are always moving and form different materials by joining together. -
John Dalton
John Dalton’s theory is that atoms make up everything and they cannot be created, divided, or destroyed. He said that atoms of the same element are all exactly alike and different elements are different. His theory also said that different atoms join together to make new substances. -
J. J. Thomson
Using a Cathode Ray he discovered that a positive plate would attract an invisible beam. He said that the beam has to have a negative charge to go to the positive plate. He called the particles corpuscles, but today they are called electrons. He also said that atoms have no overall charge so to balance the negative charge you have to add a positive charge. His model of the atom became known as the plum-pudding model. The model was filled with positive and negative electrons throughout the atom. -
Ernest Rutherford
When Ernest Rutherford aimed positively charged particles at a gold foil sheet, he was surprised because some were deflected or bounced back. Then in 1911 he revised his theory by saying that the nucleus of the atom was 100,00x smaller than the entire atom. He said the atom has a small, positively charged nucleus, and most of the it is empty space, where the electrons travel. Also the electrons travel around the nucleus, like planets around the sun, but the exact placement can’t be described. -
Niels Bohr
Niels Bohr discovered that the electrons travel around the nucleus in definite paths and that they are located in levels and the electrons jump between the levels. -
Modern Model
Today we know that there is a lot of empty space where electrons are likely found, called electron clouds.
