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Dalton's Theory

all matter is made up of individual particles called atoms, which cannot be divided.


noticed that the ratio of the masses of elements in a compound is always the same.


like charges


opposite charges


provided evidence that atoms are made of even smaller particles

Thomson's Model

Plum Pudding Model or the Chocolate Chip Ice Cream Model


Discovered the Nucleus


dense, positively charged mass located in the center of the atom.

Subatomic Particles

protons, electrons, and neutrons


positively charged subatomic particle found in the nucleus of the atom


a negatively charged subatomic particle found in the space outside the nucleus


a neutral subatomic particle found in the nucleus of the atom

Protons and Neutrons

have a similar mass

Atomic Number

is equal to the number of protons in an element

Mass number

is the sum of the protons and neutrons in the nucleus of an atom

Number of Neutrons

Equals the Mass Number minus the Atomic Number


atoms of the same element that have differnt numbers of neutrons and different mass numbers

Bohr's Model

the atom is like the solar system and the planets orbiting the sun

Energy levels

The possible energies that electrons in an atom can have.

energy is absorbed

Electrons move up an energy level

energy is released

Electrons move down an energy level

Electron Cloud

most likely locations for electrons in an atom


region of space around the nuclues where an electron is likely to be found

Ground state

when all electron in an atom have the lowest possible energies

Ground state

The most stable electron configuration

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