Unit 2 Atomic Theory

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Excited State

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A state of an atom or molecule in which it has more energy than in its ground state.

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Gold Foil Experiment

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An experiment conducted by Ernest Rutherford that led to the discovery of the atomic nucleus.

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Mass Number

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The total number of protons and neutrons in an atomic nucleus.

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Bohr Model

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A model of the atom in which electrons orbit the nucleus in paths of fixed energy.

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Proton

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A positively charged subatomic particle found in the nucleus of an atom.

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Neutron

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A subatomic particle found in the nucleus of an atom that has no charge.

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Atomic Number

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The number of protons in the nucleus of an atom, which determines the element's identity.

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Atom

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The smallest unit of an element, consisting of protons, neutrons, and electrons.

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Electron

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A negatively charged subatomic particle that orbits the nucleus of an atom.

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Valence Shell

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The outermost shell of an atom that contains electrons involved in chemical bonding.