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Democritus' Theory
http://plato.stanford.edu/entries/democritus/
• All things are composed of invisible tiny particles of matter, which can’t be destroyed. -
John Dalton's Theory
http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/the-path-to-the-periodic-table/dalton.aspx
• Described tiny indivisible particles called atoms.
• Atoms can’t be divided or destroyed.
• Atoms can join together to form molecules.
• Atoms of one element are all the same. -
J.J. Thompson's Theory
http://www.nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-bio.html
• Atoms contain electrons, which have a negative charge.
• Atoms are solid with electrons and protons randomly placed through them. -
Ernest Rutherford's Theory
<a href='' >http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html</a>
• Atoms have a dense nucleus which contains protons, and most of the rest is empty space.
• Electrons orbit around the nucleus like planets around the sun. -
Niels Bohr's Theory
http://www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html
• Electrons are arranged in layers or shells around the nucleus.
• The shells have different energy levels, and electrons fill up the lowest levels first. -
James Chadwick's Theory
http://www.nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html
• The nucleus also contains neutrons, which are unchanged particles with a similar mass to protons.
