1. Chemical Formulas: The Basics

2. Subscripts in Chemical Formulas numbers inside formulas numbers inside formulas lowered below line of type lowered below line of type show # of atoms of each element show # of atoms of each element

3. Rules for Subscripts in Formulas No subscript – understood to be 1 No subscript – understood to be 1 Subscripts refer to element immediately preceding number [Remember – every element symbol starts with capital letter] Subscripts refer to element immediately preceding number [Remember – every element symbol starts with capital letter] Subscripts after parentheses refer to everything inside ( ) Subscripts after parentheses refer to everything inside ( )

4. Chemical Formulas H 2 O has: 2 hydrogens and 1 oxygen H 2 O has: 2 hydrogens and 1 oxygen NH 3 has: 1 nitrogen and 3 hydrogens NH 3 has: 1 nitrogen and 3 hydrogens CH 4 has ? CH 4 has ? CO 2 has ? CO 2 has ? AgNO 3 has ? AgNO 3 has ? 1 carbon and 4 hydrogen 1 carbon and 2 oxygen 1 silver, 1 nitrogen, 3 oxygen

5. # atoms in formulas Al(NO 3 ) 3 Al(NO 3 ) 3 Al = Al = N = N = O = O = Total = Total = Subscript outside ( ) multiplied by subscript inside ( ) = # of atoms1 1 x 3 = 3 3 x 3 = 9 13 atoms

6. Coefficients Numbers in front of formulas Numbers in front of formulas Refers to everything following in formula Refers to everything following in formula No coefficient? It’s understood to be 1 No coefficient? It’s understood to be 1

7. Coefficients 2H 2 O means 2(H 2 O) 2H 2 O means 2(H 2 O) To count atoms - To count atoms - multiply: coefficient x subscript multiply: coefficient x subscript 2 x 2 = 4 H’s 2 x 2 = 4 H’s 2 x 1 = 2 O’s 2 x 1 = 2 O’s

8. Hydrates group of salts that have water molecules stuffed in their empty spaces group of salts that have water molecules stuffed in their empty spaces Ex: CuSO 4  5H 2 O Ex: CuSO 4  5H 2 O  means “is associated with” or “included”  means “is associated with” or “included” DOES NOT refer to multiplication DOES NOT refer to multiplication Not a true chemical bond: Not a true chemical bond: structure is definite so structure is definite so # empty spaces is definite & # empty spaces is definite & # water molecules is definite # water molecules is definite

9. CuSO 4  5H 2 O Count up the atoms! Count up the atoms! 1 x Cu 1 x S 4 x O 10 x H 5 x O total = 21 atoms

10. 5[CuSO 4  5H 2 O] Count up the atoms! Count up the atoms! 5 x Cu 5 x S 20 x O 50 x H 25 x O total = 105 atoms Coefficients x Subscripts