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        | the smallest unit of an element that maintains the chemical properties of that element |  | 
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        | a substance that cannot be separated or broken down into simpler substances by chemical means; all atoms of an element have the same atomic number |  | 
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        | an electron that is found in the outermost shell of an atom and that determines the atom's chemical properties |  | 
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        | a substance made up of atoms of two or more different elements joined by chemical bonds |  | 
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        | a group of atoms that are held together by chemical forces; a molecule is the smallest unit of matter that can exist by itself and retain all of a substance's chemical properties |  | 
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        | an atom, radical, or molecule that has gained or lost one or more electrons and has a negative or positive charge |  | 
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        | the force that holds molecules of a single material together |  | 
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        | the attractive force between two bodies of different substances that are in contact with each other |  | 
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        | a homogeneous mixture throughout which two or more substances are uniformly dispersed |  | 
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        | any compound that increases the number of hydronium ions when dissolved in water; acids turn blue litmus paper red and react with bases and some metals to form salts |  | 
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        | any compound that increases the number of hydroxide ions when dissolved in water; bases turn red litmus paper blue and react with acids to form salts |  | 
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        | a value that is used to express the acidity or alkalinity (basicity) of a system; each whole number on the scale indicates a tenfold change in acidity; a pH of 7 is neutral, a pH of less than 7 is acidic, and a pH of greater than 7 is basic |  | 
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        | a solution made from a weak acid and its conjugate base that neutralizes small amounts of acids or bases added to it |  | 
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        | a class of molecules that includes sugars, starches, and fiber; contains carbon, hydrogen, and oxygen |  | 
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        | a fat molecule or a molecule that has similar properties; examples include oils, waxes, and steroids |  | 
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        | an organic compound that is made of one or more chains of amino acids and that is a principal component of all cells |  | 
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        | a compound of a class of simple organic compounds that contain a carboxyl group and an amino group and that combine to form proteins |  | 
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        | an organic compound, either RNA or DNA, whose molecules are made up of one or two chains of nucleotides and carry genetic information |  | 
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        | an organic compound that consists of a sugar, a phosphate, and a nitrogenous base; the basic building block of a nucleic-acid chain |  | 
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        | deoxyribonucleic acid, the material that contains the information that determines inherited characteristics |  | 
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        | ribonucleic acid, a natural polymer that is present in all living cells and that plays a role in protein synthesis |  | 
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        | adenosine triphosphate, an organic molecule that acts as the main energy source for cell processes; composed of a nitrogenous base, a sugar, and three phosphate groups |  | 
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        | a substance or molecule that participates in a chemical reaction |  | 
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        | a substance that forms in a chemical reaction |  | 
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        | the minimum amount of energy required to start a chemical reaction |  | 
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        | a molecule, either protein or RNA, that acts as a catalyst in biochemical reactions |  | 
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        | on an enzyme, the site that attaches to a substrate |  | 
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        | a part, substance, or element that lies beneath and supports another part, substance, or element; the reactant in reactions catalyzed by enzymes |  | 
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