Atomic Models (Amy Burt)

Democritus

Oct 30, 1000

Democritus believed that all matter was made of really small atoms that could not be divided. The atoms in liquids, for example, were round and smooth,but atoms in solids were rough and prickly.

Aristotle

Oct 30, 1000

Exsisted in 500 B.C. Aristotle believed that all substances were made with only four elements. Those elements would include; Earth, Air, Fire, and Water. These combinations had four qualities, which would include; Hot, Cold, Dry, and Wet. Fire was a combination of hot and dry. Water was a combination of cold and wet.

John Dalton

Oct 30, 1803

Dalton predicted that the atoms of any element are different from the atoms of all other elements. In his theory, all the atoms of a given element are identical. Isotopes of an element have the same atomic number but different mass numbers because they have different numbers of neutrons.

George Johnstone Stoney

Oct 31, 1894

He wrote a letter titled the “Electron”, or Atom of Electricity to the editors of the Philosophical magazine. He calls a definite quantity of electricity E¬r which is later developed to be an ‘electron’. Also, he estimates the mass of an electron. We know the mass on an electron and that it is a definite quantity of electricity.

J.J Thomson

Oct 30, 1897

Thomson hypothesised that the beam was a stream of charged particles that interacted with the air in the tube and caused the air to glow. Thomson concluded that the particles in the beam had a negative charge because they were attracted to the postive plate. An atom is a neutral, meaning it has neither a negative nor a postive charge.

Max Planck

Oct 31, 1900

Max developed the Quantum theory. He attempted to draw conclusions from the heat radiation to the radiating atom. The discovery of quanta changed the idea of physics, because it showed that established ideas about the nature of radiation and energy were wrong.

Hantaro Nagaoka

Oct 31, 1904

Thinks that an atom has a central nucleus. Electrons move in orbits like the rings around saturn.

Ernest Marsden

Oct 31, 1909

Ernest Marsden worked with Ernest Rutherford and Hans Geiger to discover the deflection paths of alpha particles. Marsden was an undergraduate when he began working with Rutherford and Geiger to determine whether alpha particles can be scattered through a large angle. In 1909 the team discovered that they could, and this became the basis for the discovery of the proton. Used an instrument callled an Alpha.

Ernest Rutherford

Oct 30, 1911

Ernest discovered that uranium emits fast-moving particles have a postive charge. According to Rutherford's model, all of an atom's positive charge is concentrated in its nucleus.

Niels Bohr

Oct 31, 1913

Niels Bohr applies quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits defined by their angular momentum. This led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit. Bohr's model focused on electrons,

Louis de Broglie

Oct 31, 1924

He proposed in 1924 that electrons could behave as waves under some conditions, a finding that helped scientists understand that the atom didn't behave like the solar system because electrons do not move in regular orbits. Showed the motions of waves,

Erwin Schrödinger

Oct 31, 1926

Edwin Schrodinger stated that rather than electrons being distributed within an electron configuration of shells and energy levels, they were arranged in orbitals which were systematically distributed within Electron Clouds. He defined an orbital as: The region of space that surrounds a nucleus in which two electrons may randomly move. He works to represent the electron cloud model.

James Chadwick

Oct 31, 1932

James Chadwick proved the existence of neutrons. As uncharged particles in atoms, neutrons play a key part in nuclear fission, or the splitting of atoms. His experiments with neutrons were succesful.