National 5 Chemistry Unit 1 Definitions - from SQA Spec

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Catalyst

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Substances that speed up chemical reactions but can be recovered chemically unchanged at the end of the reaction.

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Isotope

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Atoms with the same atomic number but different mass numbers. (atoms with the same number of protons but different number of neutrons)

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Covalent Bond

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When two positive nuclei are held together by their common attraction for a shared pair of electrons.

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Ionic Bond

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Electrostatic attraction between positive and negative ions.

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Spectator Ions

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Ions that remain unchanged by a reaction.