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Period: 460 BCE to 370 BCE
Democritus (Greece)
Democritus found out that matter was made out of atoms, which move through an empty space.
Atoms are solid, homogeneous, indestructible and invisible.
All matter is composed of indivisible particles termed "atomos", which in greek means "indivisible". -
John Dalton (England)
Dalton created the atomic theory, which states the following points.
1. Matter is composed of extremely small particles called atoms.
2. An element is composed of atoms of the same type only.
3. Different atoms combine in simple whole-number ratios to form compounds.
4. In a chemical reaction, atoms are separated, combined, or rearranged, but never destroyed. -
Joseph John Thomson (England)
Thomson discovered the negative electrons inside of the atoms.
Plum pudding model. -
Ernest Rutherford (New Zealand)
Rutherford discovered the atomic nucleus and the proton, both with a positive charge.
He also experimented on a tin gold leaf and concluded that atoms are composed of a nucleus and an empty space where electrons move. -
Niels Böhr (Denmark)
Bohr published a theory of atomic structure associating the electrons' arrangement inside the atom, in fixed orbits around the sun. For this he won the Nobel Prize in 1922.
He also assigned a quantum number for each orbit. -
Erwin Schrödinger (Austria)
Schrödinger created the quantum mechanical model, in which he stated that electrons occupy only certain orbitals around the nucleus and that these orbitals are called "stationary" orbitals.
He also found calculated energy sublevels and orbitals, and that each orbital has an energy associated.
He introduced the electron cloud model as well. -
Werner Heisenberg (Germany)
He created the uncertainty principle: "The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa". -
James Chadwick (England)
He proved the existence of neutrons and discovered that the atomic number is determined by the number of protons in the nucleus of the atom.