Ionic Formulas Rule of Eight -ionic compounds (metal and nonmetal) tend to form atoms that together have a total of 8, 16, or 24 valence electrons which makes them similar to a noble gas which is very stable Examples: If the valence electrons add up to eight, leave as is. To combine Na and Br: Na = 1 e- and Br = 7 e-  NaBr = 8 e- If they don’t, change the number of each element until you get 8, 16, or 24. To combine Be and F: Be = 2 e- and F = 7 e- mulitply F x 2. Be = 2 e- and F (x2) = 14 e-  BeF2 = 16 e-

Ionic Formulas Nobel gases are an exception. They already have 8 valence electrons, so they are happy the way that they are. =

Ionic Formulas Ions -metals give up electrons -nonmetals take electrons -when metals give up valence electrons, they are left with a slightly positive charge -when nonmetals take valence electrons, they are left with a slightly negative charge For example: metals: Na+1 or Mg+2 nonmetals: O-2 or F-1

Ionic Formulas -when combining metals and nonmetals, total charge should equal zero! -if combining them doesn’t equal zero, change the number of atoms For example: To combine Na and F: Na+1 + F-1 = NaF and total charge = 0 To combine Na and O: Na+1 + O-2 = -1  NO GOOD! Na+1 (x 2) + O-2 = Na2O and total charge = 0

Ionic Formula Practice Using your Common Ion Chart, put together the following monatomic and polyatomic ions into compounds. 1. Al and NO3 2. Fe (III) and Cl 3. Ti (IV) and O 4. Ca and CO3 5. Cu (II) and NO2 6. Sn (IV) and CN 7. Ba and PO4 8. Ag and SO3 9. Ni and Se 10. Sn (II) and PO4 11. Li and OH