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450 BCE
Democritus Cuts Matter
Around 450 BC, Greek philosopher, Democritus, wonders what happens when you cut matter into smaller pieces until it can no longer be cut. He called these uncuttable pieces "atomos" later called, atoms. -
Period: 450 BCE to
History of the Atom
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350 BCE
Aristotle Rejects Democritus
At about 350 BC, 100 years after Democritus's idea of atoms, Aristotle rejects it and Aristotles ideas were accepted for nearly 200 years. -
Dalton Revives Democritus
Around 1800, Dalton brings back Democritus's idea of atoms. Though, Dalton thought that atoms represented tiny solid particles of matter he was wrong. His experiments included him studying the pressures of gases where he concluded that gases were made of tiny particles that constantly move around. -
Electrons are Discovered
In the year 1897, scientist J.J. Thomson discovers electrons while looking inside atoms. At Cambridge University, Thomson was experimenting with currents of electricity inside empty glass tubes. He noticed rays inside the atom which turned out to be smaller pieces inside of the atom. He called them "corpuscles". He then realized that the rays are made up of electrons which are small, negatively charged particles that are fundamental parts of every atom. -
Rutherford Discovers the Nucleus
A physicist from New Zealand named Ernest Rutherford discovered the Nucleus of an atom in the year 1899. He realized that some particles are positively charged, so he called them the alpha particles. In 1911 he decided to experiment with these particles. He aimed a beam of alpha particles at a very thin sheet of gold foil. He placed a screen that glowed when alpha particles hit it. The alpha particles passed through. This is called back scattering. http://www.light-science.com/chadwick.html -
Bohr Contributes to the Atomic Structure
Around 1922, scientist Niels Bohr helps to contribute to the knowledge of atomic structure. He developed the Bohr Model which shows what an atom looks like and what it consists of. In that, he said that energy levels of electrons are discrete and that the electrons revolve in orbits around the nucleus but can jump from one energy level to another. He worked with JJ Rutherford at Cambridge also. He also introduced the quantum theory. He won the Nobel peace prize for his discoveries.
