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200
440 B.C.-Aristotle
He disagreed with Democritus idea. He believed that you would never end up with a particle that could not be cut. He ha such a strong influence on people's ideas that for a long time, most people thought he was right. -
200
440 B.C.-Demucritus'
Democritus thought that you could cut something in half until there could not be cut anymore. He called the particle an atom. He also said that all atoms are small, hard particles, he also thought that atoms were made of a single material formed into different shapes and sizes. -
John Dalton
John Dalton was a British chemist and schoolteacher; he published the atomic theory in 1803. It included:1.- all substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed.2.- Atoms of the same element are exactly alike and atoms of different elements are different 3.- atoms join with other atoms to make new substances -
J.J. Thomson
Thomson showed that there was a mistake in Dalton's Theory. Thomson discovered that there are small particles inside the atom. This means that atoms can be divided into smaller parts -
Schrodinger and Heisenberg
They further explained the nature of electrons in the atom. Electrons do not travel in definite paths as Bohr suggested. The theory there are regions inside an atom were electrons are likely to be found. This is called an electron cloud. -
Ernest Rutherford
He designed an experiment to study the parts of an atom. He aimed a beam of small, positively charged particles at a thin sheet of gold foil. He put a special coating behind the foil. The coating glowed when hit by the positively charged particles, so then he can see where the particles go. -
Ernest Rutherford
He made a new model of the atom. He proposed that in the center of the atom is a tinny, extremely dense, positively charged particle called nucleus. He reasoned that positively charged particles that passed close by nucleus were pushed away by the positive charges in the nucleus. -
Bohr
He was a scientist who worked with Rutherford. His result led him to propose that electrons move around the nucleus in certain paths, or energy levels.
