16.2 Chemical Formulas and Oxidation Numbers All compounds have an electrical charge of zero (they are neutral). An oxidation number indicates the charge on the atom (or ion) when electrons are lost, gained, or shared in chemical bonds.

Creating Ionic Compounds (metal + nonmetal) Determine what ions each element forms (by knowing how many valence electrons it has – oxidation number) & write in ion notation form. Crisscross their charges, but drop the +/- and this will be how many of each you need to form a compound. Ex: Ca2+ reacts with Cl1- and forms CaCl2

Naming Compounds Ionic (metal + nonmetal) Write the name of the metal like normal Write the name of the non-metal, but change the ending to –ide.

Examples: a. NaCl = sodium chloride (chlorine becomes chloride) b. FeO = iron oxide (oxygen becomes oxide) c. Li2S = lithium sulfide

4. Transition Metals: Transition metals can form multiple ions Use a Roman Numeral after the metal to denote its charge Examples: Iron (II) Oxide: FeO Iron (III) Oxide: Fe2O3

B. Covalent (two non-metals) If there is only one atom of the first element, write its name like normal. 2. If there is a subscript for the first element, write the prefix for that subscript attached to the normal element name.

Prefixes 1 = mono 6 = hexa 2 = di 7 = hepta 3 = tri 8 = octa 4 = tetra 9 = nona 5 = penta 10 = deca

N2P5 = Dinitrogen Pentaphosphide The 2nd element always gets a prefix and the element always gets the ending –ide. a. examples CO2 = Carbon Dioxide (first element gets no prefix, second element gets prefix and ending) N2P5 = Dinitrogen Pentaphosphide (both get prefixes, second element also changes to –ide)

C. Compounds with polyatomic ions. 1. Identify the polyatomic ion C. Compounds with polyatomic ions. 1. Identify the polyatomic ion using a chart. A polyatomic ion is an ion with more than one atom.

2. If the ion is at the end, write the first element normal, then C. Compounds with polyatomic ions. 2. If the ion is at the end, write the first element normal, then the polyatomic’s name ex: CaCO3 = Calcium Carbonate

ex: NH4Cl = Ammonium Chloride C. Compounds with polyatomic ions. 3. If the ion is at the beginning, write the polyatomic’s name, then the last element with the “-ide” ending. ex: NH4Cl = Ammonium Chloride