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Matter and Atomic Theory (Electrons are very small particles located in…
Matter and Atomic Theory
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In an element, protons are always the same. However, the amount of neutrons can differ in each element and determine what kind of isotope it is, and the average mass number.
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During the time of ancient Greece, a Greek philosopher, named Democritus, theorized that a substance could reach a very small point and become indivisible. This is what he defined as an
atom.
During the 19th century, English chemist, John Dalton, created more widely accepted ideas about atoms. Most importantly, he stated that compounds are made up of a fixed ratio of atoms of different elements, and the reactants can cause an exothermic reaction to form a compound.
Dmitri Mendeleev was the first person to introduce a Periodic Table, and arranged elements by their distinct properties and atomic weights. Through the early Periodic Table, other scientists eventually added many new elements that were discovered later.