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460 - 370 B.C.E.
Concluded that there is a limit to how far you could divide matter. You would eventually end up with a piece of matter that could not be cut. called it an atom!
The Greek word “atomos” means not able to be divided or “indivisible.”
My theory says...
Atoms are small hard particles
Made of a single material formed into different shapes and sizes
They are always moving
They form different materials by joining together. -
350 B.C.E
there are five elements:
earth
wind
water
fire
ether
These elements make up all substances and they all move to the center of the universe --- which is Earth of course. -
Dalton’s atomic model is called the “Billiard Ball Model.” All substances are made up of atoms which are small particles that cannot be created, divided, or destroyed.
Atoms of the same element are exactly alike and atoms of different elements are different.
Atoms join with other atoms to form different substances
In chemical reactions, atoms are combined, separated, or rearranged. -
This was a glass tube with two electrodes connected to a battery. The vacuum sealed tube allowed Crookes to see a pathway where the electrons traveled!
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I decided to organize the elements discovered thus far by their properties. This was the beginning of the modern periodic table! My periodic table organizes the known elements by their properties of atomic weight and valance (valance electrons are those in the outer shell --- who remembers the "octet rule?")
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Thomson took Crookes’ tube and used a magnet to bend the ray. The ray bent towards the positive side of the magnet. He concluded that the ray must have had a negative charge if it was attracted to the positive side. These negative charges became known as electrons.
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An atom has a dense center called the nucleus that has a positive charge!
Most of an atom is empty space!
The nucleus has a large mass (well... compared to electrons!!!) -
Proposed that electrons move in paths at certain distances around the nucleus. Electrons can jump from a path on one level to a path on another level. Planetary Model
electrons move in circular orbits within specific energy levels -
Discovered neutrons, neutral particles in the nucleus of an atom using Joliot-Curie Experiments. I based on my theory on their experimental evidence.
