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Chemical Formulas: The Basics Subscripts in Chemical Formulas Numbers inside formulas. Smaller than the font size & lowered below the line of type. Subscripts show the number of atoms of each element in a representative unit. Rules for Subscripts in Formulas No subscript – it’s understood to be 1. Subscripts refer to the element immediately preceding them. Subscripts after parentheses refer to everything inside ( ). Chemical Formulas H2O has 2 hydrogens and 1 oxygen NH3 has 1 nitrogen and 3 hydrogens CH4 has ? 1 carbon and 4 hydrogens CO2 has ? 1 carbon and 2 oxygens AgNO3 has ? 1 silver, 1 nitrogen, 3 oxygens Al(NO3)3 has ? 1 aluminum, 3 nitrogens, and 9 oxygens No. of atoms in formulas Al(NO3)3 Al = 1 N= 1X3=3 O= 3X3=9 Total = 13 Subscript outside ( ) X subscript inside ( ) = # of atoms Hint: Look for uppercase letters! No. of atoms in formulas Mg3(PO4)2 Mg = 3 P= 2X1=2 O= 4X2=8 Total = 13 Coefficients Numbers in front of formulas Refer to everything in the formula immediately following No coefficient? It’s understood to be 1. Coefficients 2H2O means 2(H2O) To count atoms take coefficient X subscript 2 X 2 = 4 H’s 2 X 1 = 2 O’s Hydrates A group of salts that have water molecules stuffed in the empty spaces Formulas are distinctive Ex: CuSO45H2O means “is associated with” or PLUS Not a true chemical bond, but the structure is definite so the number of empty spaces is definite and the number of water molecules is definite CuSO45H2O Count up the atoms! 1 X Cu 1XS 4XO 10 X H 5XO 5[CuSO45H2O] Count up the atoms! 5 X Cu 5XS 20 X O 50 X H 25 X O Coefficients X Subscripts