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Added a history of the atomic theory
Atoms of the same element that have different numbers of neutrons are known as [[isotope]]s. Some isotopes are more stable than others, and occur more often in nature, but there is no "standard" number of neutrons in a given element. The atomic weight of an element is a weighted average of the number of neutrons and protons (number of protons remains constant in a given element) in all naturally occurring isotopes. Many isotopes are [[radioactive]] and [[radioactive decay|decay]] over time.
Atoms of the same element that have different numbers of neutrons are known as [[isotope]]s. Some isotopes are more stable than others, and occur more often in nature, but there is no "standard" number of neutrons in a given element. The atomic weight of an element is a weighted average of the number of neutrons and protons (number of protons remains constant in a given element) in all naturally occurring isotopes. Many isotopes are [[radioactive]] and [[radioactive decay|decay]] over time.
==History of the Atomic Model==
The early Greek philosophers [[Democritus]] and [[Leucippus]] first proposed that all matter in the universe consisted of particles, which are the smallest units of [[matter]], though [[Aristotle]] used his fame to convince the [[scientific community]] that matter consisted of various ratios of [[earth]], [[fire]], [[water]], and [[air]], which can exist in any quantity. This mislead them for centuries.
[[John Dalton]] developed a realistic atomic theory based on four principles: that all matter is composed of atoms, that each element's atoms are of one size, atoms combine chemically to form compounds, and chemical reactions occur when atoms are joined or separated. His theory relied on [[Antoine Lavoisier|Lavoisier's]] [[Law of the conservation of mass|Law of Conservation of Mass]] and [[Joseph Proust|Joseph Proust's]] [[Law of definite proportions|Law of Definite Proportions]].
[[J. J. Thompson]] later developed the [[Plum Pudding]] Model, a result of his discovering the [[electron]] using [[cathode ray tube|cathode ray tube]]. [[Ernest Rutherford]] later discovered in his [[gold foil experiment]] that the atom was mostly empty space, with a nucleus of protons in the center. [[James Chadwick]] discovered the neutron and complexities of the nucleus, paving the way for [[nuclear fission]].
==See also==
==See also==