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440
(BCE)Aristotle disagrees with Democitus
Aristotle, a different Greek philosopher, disagreed with Democritus’s ideas. He believed that you could never end up with a particle that could not be cut. He had a strong influence on people’s ideas, so most people thought he was right. -
440
(BCE)Democritus discovers the Atom(Timetoast doesn't register BCE)
Democritus thought that if you cut a substance over and over again you would eventually end up with a particle that could not be cut. He called this particle an atom. The word atom is from the Greek word atomos, meaning “Indivisible.” Democritus said that all atoms are small, hard particles and He thought that atoms were made of a single substance formed into different shapes and sizes to make different things. -
John Dalton devolped his Atomic theory
John Dalton, who was a British chemist and schoolteacher, experimented with different substances. His results suggested that elements combine in certain proportions because they are made of single atoms. Dalton published his atomic theory in 1803. His theory stated the following ideas:
• All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed.
• Atoms of the same element are exactly alike, and atoms of different elements are different -
J. J. Thomson showed that there was a mistake in Dalton’s theory
A British scientist named J. J. 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 even smaller particles.
Thomson experimented with a cathode-ray tube. He discovered that a positively charged plate attracted the beam. Thomson concluded that the beam had negative electric charges. He concluded that these negatively charged particles called electrons are present in all Atoms. -
Ernest Rutherford decided to test Thomson’s theory
A former student of Thomson’s named Ernest Rutherford studied the atom by testing Thomson's Theory. He aimed a beam of positively charged particles at a sheet of gold foil with a special coating behind it. The coating glowed when hit by the positively charged particles. Rutherford could then see where the particles went after hitting the gold. Rutherford started with Thomson’s idea that atoms "Blobs" of matter. He expected the particles to go through the foil, but the atoms bounced off the foil. -
Bohr recieved a Nobel prize for his atomic model
Bohr's contribution to physics was the atomic model. Bohr's model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. Bohr discovered that electrons travel in orbits around the nucleus and he discovered that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of and element that the number of electrons in the outer orbit determines the properties of the element. -
Schrodinger
Erwin Schrödinger, an Austrian physicist, took the Bohr model further by using mathematical equations to find the likelihood of finding an electron in a certain position. This model is known as the quantum mechanical model. This model predicts the odds of the location of the electron. This model can be shown as a nucleus surrounded by an electron cloud. Where the cloud is most dense the more likely the electons are there and where the cloud is the least dense the less likely electrons are there. -
Heisenburg
Werner Heisenberg was a German theoretical physicist who made wonderful contributions to quantum theory. Heisenberg made the “matrix mechanics” formulation of quantum mechanics. Matrix mechanics was the first complete and correct definition of quantum mechanics, and it extended the Bohr model of atoms by describing how the quantum jumps occur and by interpreting the physical properties of particles as matrices that evolve over time.
