Chemical Formulas: The Basics

Subscripts in Chemical Formulas Numbers inside formulas Found below line of type Subscripts show # of atoms of each element in formula

Rules for Subscripts in Formulas No subscript: understood to be 1 Subscripts refer to element immediately preceding number Remember – every element symbol starts with upper case letter Subscripts after parentheses refer to everything inside ( )

Chemical Formulas H2O: 2 hydrogen and 1 oxygen NH3: 1 nitrogen and 3 hydrogen CH4 has ? CO2 has ? AgNO3 has ? 1 carbon and 4 hydrogen 1 carbon and 2 oxygen 1 silver, 1 nitrogen, 3 oxygen

Hint: Look for uppercase letters! Subscript outside ( ) multiplied by subscript inside ( ) = # of atoms Al(NO3)3 Al = N = O = Total = 1 1 x 3 = 3 3 x 3 = 9 13 atoms Hint: Look for uppercase letters!

Coefficients Numbers in front of formulas Refers to everything immediately following in formula No coefficient? understood to be 1

Coefficients 2H2O means H2O and H2O To count atoms - multiply: coefficient x subscript 2 x 2 = 4 H’s 2 x 1 = 2 O’s

Hydrates group salts that have water molecules stuffed in their empty spaces Formulas are distinctive Ex: CuSO45H2O  means H2O “is associated with” or “included” Does NOT refer to multiplication Not true chemical bond: structure is definite number empty spaces is definite number water molecules is definite

CuSO45H2O Count up the atoms! 1 Cu 1 S 4 O + 5x1 O = 9 O 5x2 H =10 H total = 21 atoms

5CuSO45H2O Count up the atoms! 5 = Cu 5 = S 5x4 O + 5x5x1 O = 45 O 5x5x2 H = 50 H total = 105 atoms