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Period: 490 BCE to
Timeline of atomic Models
The time line of all 5 scientists' atomic models -
460 BCE
Democritus
Democritus was a Greek philosopher who proposed the idea that matter is made of tiny, indivisible, indestructible particles that he called atomos, from which the English word atom is made form. Unfortunately, this idea was rejected because he didn't have the necessary equipment to test his ideas. His model was just a plain sphere. He had developed the concept of the atom. -
John Dalton
Dalton's theory is called Dalton's Atomic Theory. His ideas were:
All elements are made of atoms. It's impossible to destroy them
Atoms of the same elements are alike.
Atoms of different elements are different.
Atoms of different elements combine to form a compound. These atoms have to be in definite whole number ratios.
These were his theories of atoms and matter. He claimed that compounds are made of 2 or more different kinds atoms. -
J.J. Thompson
J.J. Thompson was an English scientist. He was experimenting with gas discharge tubes, when he notices a movement in a tube. He called it cathode rays. The rays moved from the negative end of the tube to the positive end. This is because opposite rays attract each other. He notices the rays were made of negatively charged particles. In this process, he discovered electrons, that are negatively charged. -
Lord Ernest Ruthford
Ruthford conducted an experiment called the gold foil experiment. To do this experiment, he use a sheet of gold foil, and he used a device to shoot alpha particles at the gold foil. Most of the particles passed through the gold foil like the foil was not there. Some were deflected as if they had hit something. The 2 major discoveries he made are that atoms are mostly empty space, and atoms are made of a small positive nucleus and that positive nucleus repels positive alpha particles. -
Niels Bohr
Bohr was a Danish physicist. He made a model of the atom that is similar to the model of out solar system. The electrons go around the nucleus like planets orbit around the sun. He discovered that all electrons have their own energy levels. The energy of electrons goes up from level 1 to other levels. When they lose energy, they lose a level, and when they gain energy, they go up a level. Each level can hold a certain amount of electrons.
