All matter is composed of indivisible atoms.
An element is a type of matter composed of only one kind of atom. All atoms of the same element have the same properties.
A compound is composed of atoms of two or more elements combined chemically in fixed proportions.
During a chemical reaction reactant atoms rearrange and combine to form new substances.
J. J. Thomson
Discovered electrons - negatively charged particles inside an atom
Proposed plum-pudding model = negatively charged electrons are embedded in a positively charged sphere
Did the Gold Foil Experiment where he bombarded thin foil foil with alpha particles (positively charged) and observed that most alpha particles went through the foil and some deflected back. He concluded that:
Most of the atom is empty space(99.95% or more)
There is a dense, small, nucleus that is positively charged
Electrons move outside the nucleus
Electrons move in circular orbits at fixed distances from the nucleus
Louis de Broglie
Proposed that particles such as electrons have wavelike properties
Developed a mathematical equation to describe the motion of electrons in an atom
Confirms the existence of neutrons (neutral charge) which are located inside the nucleus along with protons.
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