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        | loss of an electron. may happen during some chemical reaction |  | 
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        | Term 
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        | gain of an electron. may happen during some chemical reaction |  | 
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        | refers to a group of atoms held together by energy in a stable association |  | 
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 | Definition 
 
        | composed of two or more different types of atoms bond together |  | 
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 | Definition 
 
        | are formed because ions of opposite charge attract one another |  | 
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        | Term 
 | Definition 
 
        | are formed when two or more atoms share pairs of valence electrons |  | 
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        | Term 
 | Definition 
 
        | attractive force between the hydrogen attatched to an electronegative atom of one molecule and an electronegative atom of a different molecule. 
 ---easiest to make, easiest to break
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        | Term 
 | Definition 
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        | Term 
 | Definition 
 
        | a change in mass or distance |  | 
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 | Definition 
 
        | chemical reactions in cells cannot start without help.  gets the reaction started |  | 
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 | Definition 
 
        | produce more energy than they use |  | 
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 | Definition 
 
        | use more energy than they produce |  | 
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        | Term 
 | Definition 
 
        | molecules based on carbon and hydrogen |  | 
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 | Definition 
 
        | molecules not based on carbon and hydrogen |  | 
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 | Definition 
 
        | essential molecules obtained from food |  | 
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 | Definition 
 
        | all body cells except sex cells |  | 
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        | Term 
 
        | phospholipid bilayer *hydrophillic heads-toward watery environment, both sides
 *hydrophobic fatty-acid tails-inside membrane barrier to ions and water soluble compounds
 |  | Definition 
 
        | double layer of phospholipid molecules *2 characteristics
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