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Theories on Atomic Structure
By: Allison McDowell, Kaniya McDonald, and…
Theories on Atomic Structure
By: Allison McDowell, Kaniya McDonald, and Anya Rassolov
Ancient Greek Beliefs
Democritus
Believed atoms were solid, uniform, incompressible, and indestructible. moved at infinite numbers through empty space until stopped. Believed atoms were a solid ball.
- He could not explain what held atoms together which is why his theory was rejected my many philosophers
- But theorized that all material bodies were made up of atoms
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Dalton
Dalton was the first to try and explain all properties of atoms. His theory was inspired by Democritus. His theory had five parts:
He put forth the idea that toms could not be created or destroyed, even in chemical reactions.
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Different elements are unique from each other, and their atoms are not the same, either.
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He believed that compounds (made of two or more elements) were combinations of two or more different atoms.
Cons:
At this point in time, we now know that atoms are not indivisible - the tiny nucleus is in the center, whereas the electrons orbit around the outside. They are mostly empty space, unlike what he had thought and described with his model.
Additionally, not all atoms in an element are the same - different isotopes have different numbers of neutrons (ex: deuterium)
Pros:
Aside from the two main cons and the errors in the model, Dalton's theory is quite accurate, and laid the foundations of more modern atom theories.
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Rutherford
- First one to talk about there being a nucleus
- "positively charged" "all mass is concentrated" electrons circle nucleus from a distance, like planets to the sun
- empty space between the nucleus and electrons are most of the atom's volume.
- But failed to explain the stability of electrons in a circular path
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Bohr
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"only some physical quantities only take discrete values"
- explained the stability of an atom
- His model was very limited in terms of size; poor spectral predictions
Einstein
"Any liquid is made up of molecules. " "random ceaseless motion" - Invisible in 1905 - Mathematically proved atoms existed.
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JJ Thomson
Thomson's strong points of his theory were that he introduced that atoms have charged particles, he discovered electrons.
He proposed that an atom was a sphere and negative charges were floating inside of the positively charged atom. (Plum Pudding theory)
Thomson's weak points of the plum pudding model was that he believed that electrons were on the inside of atoms
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