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300
Aristotle's Theory
Many people followed the teachings of Aristotle. When he attempted to prove that all matter was made from the four elements in 300 B.C., it caused Democritus's theory about atoms to be overlooked and dismissed for so many years. -
420
The idea of the atom was invented.
Leucippe of Milet invented the notion of the atom and that it was indivisible in 420 B.C. -
460
The Atom was first mentioned.
Democrtius, a Greek philosopher, was the first person to propose that matter was made of atoms that could not be divided into smaller particles and wrote it down in 460 B.C. The word atom comes from the greek word atomos or atomon which means "indivisible". His theory was ignored for more than 2000 years. -
Law of Conservation of Mass was developed.
Antoine Laurent Lavoisier proposed the Law of Conservation of Mass. -
The Law of Definite Proportions was developed.
The French chemist, Joseph Proust, conducted several experiments between 1798 and 1804 that led to the development of the Law of Definite Proportions. -
The idea of the atom was accepted.
In the early 1800s, the English Chemist John Dalton performed a number of experiments that led to the acceptance of the idea of atoms and Democritus' theory. John Dalton is considered the father of modern atomic theory. -
Law of Multiple Proportions was developed.
John Dalton develpoed and explained the Law of Multiple Proportions. -
Dalton's Atomic Theory
English school teacher, John Dalton, proposed an Atomic Theory from his interest in meteorology.
1. All matter is composed of small particles called atoms.
2. Atoms of the same element are identical, but atoms of different elements differ in size, mass, and other properties.
3. Atoms cannot be subdivided, created, or destroyed.
4. Atoms of different elements combine in simple whole-numbered ratios to form chemical compounds.
5. In chemical reactions, atoms are cobined, separated, or rearranged. -
Max Planck discovered quanta.
Max Planck, a professor of theoretical physics in Berlin showed that when you vibrate atoms strong enough, you can measure the energy only in discrete units. These energy packets are called quanta. -
First explanation of the structure of the atom.
Ernest Rutherford developed the first coherent explanation of the structure of an atom. -
Modern Atomic Theory was finalized.
Many scientists contributed to the Modern Atomic Theory but the father was ultimately John Dalton. His atomic theory had to be changed after it was discovered that some of it wasn't completely correct. For example, we know now that atoms can be divided into smaller particles and a given element can have atoms with different masses. Dalton's Atomic Theory hasn't been discarded, though, only modified throughout the years to the version we have today which is Modern Atomic Theory.
