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EARLY MODELSOF THE ATOM

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WHAT’S THE MATTER?•Ancient civilizations have wondered what made up the stuff around them.•Some early ideas included natural elements like earth, air, fire and water. (Empedocles)•The Greek philosopher, Democritus, suggested that matter could be cut down into smaller pieces until you reached a single indivisible particle which he called the atom.

•As history moved along, others would experiment and observe to expand our knowledge of the structure of the atom.

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DALTON’S ATOMIC THEORY• John Dalton was a teacher that came up with his theory

of atomic structure based on the work of many scientists of his era.

• Dalton’s theory (1803) included the following:– Matter consists of definite particles called atoms.– Each element has its own type of atom.– Atoms of different elements have different properties.– Atoms of two or more different elements can combine

in specific ratios to form compounds.– Atoms cannot be created or destroyed or broken up in

a chemical change.•Future scientists would build upon

Dalton’s work to help arrive at our current understanding of atomic structure.

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THE SUBATOMIC PARTICLES• The next scientist to assist in our understanding

of atomic structure was J.J. Thomson in 1897.• Thomson used advances in technology to arrive

at his famous raisin bun model of the atom.• He said atoms were like raisin buns in that you

had a positively charged sphere with negatively charged particles called electrons – the “raisins” – scattered throughout.

•This is kind of accurate if you think about what you already know about the atom.

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RAISIN BUN 2.0• In 1911, Ernest Rutherford conducted experiments

that furthered our understanding of atomic structure.• He concluded that the atom had a nucleus that held

positive charges, which he named protons.• This nucleus was surrounded by mostly empty

space which had negatively charged particles within it.

• James Chadwick would suggest the existence of neutrons within the nucleus of the atom in 1932. The neutrons had the same mass as a proton but did not carry a charge.

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ATOMIC STRUCTURE

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THAT’S ALL FOLKS!