-
300
Aristotle
Aristotle didn’t believe that atoms were of different sizes and had regular geometric shapes. He believed everything consisted of fire, earth, air, and water. -
430
Democritus
He stated that atoms are the building blocks for all things and that atoms are tiny, indivisible, and differ only by shape and arrangement. -
John Dalton
Atomic Theory:
- All elements are composed of tiny idivisible particles called atoms.
- Atoms of the same element are identical. The atoms of any one element are different from those of any other element.
-Atoms of different elements can physically mix together or can chemically combine in simple whole-number proportions.
-Chemical reactions occur when atoms are separated, joined, or rearranged. -
Michael Faraday
Studied the effect of electricity on solutions, coined term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis. -
Dmitri Mendeleev
Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". -
G.J. Stoney
Proposed that electricity was made of discrete negative particles he called electrons. -
J.J. Thomson
Discovered electrons with a cathode ray tube. -
Max Planck
Used the idea of quanta (discrete units of energy) to explain hot glowing matter. -
Hantaro Nagaoke
Postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle. -
Robert Millikan
Determine the unit charge of the electron with his oil drop experiment. -
Ernest Rutherford
Rutherford proposed that all of the positive charge and all of the mass of the atom occupied a small volume at the center of the atom and that most of the volume of the atom was empty space occupied by the electrons. -
Henri Moseley
Rearranged the periodic table by atomic number not atomic mass. -
Aston
Discovered the existence of isotopes through the use of a mass spectrograph. -
Niels Bohr
His atomic model had atoms built up of sucessive orbital shells of electrons. -
Louis de Broglie
Discovered that electrons had a dual nature-similar to both particles and waves. -
Wolfgang Pauli
On the basis of the multiplet structure of the atomic spectra and the anomalous Zeeman effect, which was not able to be interpreted for a long time, Pauli realized that the peculiar, classically non-describable type of ambiguity of the quantum theoretical properties of the luminous electron demands for its description a fourth quantum number. -
Friedrich Hund
Hund's rule states that orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin state. -
Werner Heisenberg
He calculated the behavior of electrons, and subatomic particles that also make up an atom. -
Erwin Schrodinger
Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom. -
James Chadwick
He discovered the neutron. -
Enrico Fermi
Conducted the first controlled chain reaction releasing energy from the atoms nucleus.
