Topic: Oxidation States and Criss Cross Method Do Now: Ionic, Covalent or Metallic 1.Mg 2.MgO 3.NaCl 4.CO 2 5.H 2 O 1.Metallic 2.Ionic 3.Ionic 4.Covalent 5.Covalent

positive ion and negative ion Ionic bond is a bond between: positive ion and negative ion Metals: lose valence electrons – form cation – form cation (+ ion) Nonmetals: gain electrons anion – form anion (- ion)

Metals lose their valence electrons and nonmetals gain

IONIC BONDING Ionic compounds are electrically neutral overall Ionic compounds are electrically neutral overall 1 Ca = +2 x 1 = +2 2 Cl = -1 x 2 = -2 2 K = +1 x 2 = +2 1 S = -2 x 1 = -2 2 Cr = +3 x 2 = +6 3 O = -2 x 3 = -6

Assigning Oxidation States You can look at your periodic table. It’s listed in the topic right corner. What do you do if there is more then one?!

What to do if more then 1 oxidation state V 2 S 5 – Nonmetal = top number – So S would be -2 –V2S5–V2S5 -2 x 5 = Then determine the oxidation state of the metal that will give you the same number but positive ____ x 2 = +10+5

You try… FeO Fe=____ O= ____ Fe 2 O 3 Fe=____ O= ____

Criss-Cross Method Mg +2 and Cl -1 Mg 1 Cl 2 but if subscript is 1, forget it! MgCl 2 means 1 Mg +2 and 2 Cl -1 Crisscross and Drop

NOTE: The formula has to be in the simplest whole number ratio (this is called the empirical formular Be 2 O 2 = BeO Al 3 N 3 = AlN

Try a few formulas: Ca +2 + Cl -1 Na +1 + O -2 Cs +1 + S -2 Al +3 + Cl -1 Al +3 + Se -2 Mg +2 + F -1 Ca +2 + S -2 CaCl 2 Na 2 O Cs 2 S AlCl 3 Al 2 Se 3 MgF 2 CaS