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Aristotle ~ 332BC
Concluded that all things are made up of form and matter, which can only be changed with growth, decay, or motion -
John Dalton ~ 1787
Combined the idea pf elements with the earlier theory of the atom
Proposed 4 things:
1. Matter is made of atoms
2. Atoms cannot be divided into smaller pieces
3. All atoms of an element are identical
4. Different elements are made of different atoms -
Lavoisier ~ 1789
Stated the first version of the law of conerversion of mass, recognized and named oxygen and hydrogen, helped construct the metric system, wrote the first extensive list of elements, and discovered that mass always remains the same -
Mendeleev ~ 1860s
Arranged all 63 elements by atomic weight and organized them into groups of similar properties -
Sir William Crookes ~ 1870
He conducted an experiment containing a glass tube (cathode), two pieces of metal (electrodes), and a battery. When the battery was connected, a greenish glow would appear. He hypothesized that this green glow was caused by rays of particles. -
JJ Thomson ~ 1897
He re-conducted Crookes's experiment, adding a magnet to the list of materials. The green glow would bend towards the magnet, which ment that the green glow was made of negatively charged particles (electrons). He concluded that electrons are part of every kind of atom. -
Marie Curie ~ 1898
Called the decay process of uranium and thorium "radioactivity" and, with her husband's help, discovered the radioactive elements of polonium and radium -
Albert Einstein ~ 1905
Proposed that light energy can be absorbed or emitted only in discrete packets called quanta, explained the equivalency of mass and energy (E=mc2), and mathematically proved the existence of atoms -
Lord Ernest Rutherford ~ 1906
Along with his co-workers, he wanted to see what would happen if they fired fast moving, positively charged bits of matter (alpha particles) at a thin film of metal, like gold. The result was that some of the alpha particles were veering of at different angles. He proposed that almost all mass of an atom and its positive charge (protons) are crammed into an incredibly small region of space at the center of an atom (nucleus). -
Neils Bohr ~ 1913
Calculated exactly what energy levels orbits around a nucleus would represent for the hydrogen atom -
Moseley ~ 1913
Discovered the energy of x-rays emitted by the elements increased in linear fashion with each element in the periodic table and rearranged the periodic table by atomic number -
De Broglie
Discovered electrons had a dual nature - similar to particles and waves and he supported Einstein's discoveries -
Erwin Schrodinger ~ 1930
Viewed electrons as clouds and introduced "wave mechanics" as a mathematical model of an atom -
Democritus ~ 492BC
Created the first basis of atomic theory: the all objects are made up of little indestructible and invisible things called atoms
