1. Chapter 8: More on Classification of chemical reactions Most of chapter 8 concepts has already been covered during chapter 7 presentations 1. Just a few more additional concepts to introduce! Reactions of metals with non-metals: 1. Includes all Type I & Type II compounds 2. Can also be called an “oxidation-reduction” reaction **Oxidation-reduction reaction: a reaction that involves the transfer of electrons

2. Oxidation-Reduction reactions EX: 2Na (s) + Cl 2(g)  2NaCl (s) 1. Here is what is really going on here: a. Each of the neutrally- charged Sodium atoms, as they get closer to the neutrally-charged chlorine atoms will “give up” one of its electrons. b. The electrons that were given up by the sodium atoms will be transferred, one to each of the chlorine atoms. c. The sodium atoms, having lost one electron have now become a +1 charged ion d. The chlorine atoms, having gained one electron have now become a negative-1 charged ion

3. Oxidation-Reduction reactions Na   Na + e -  Cl  e -  Cl - Most groups of metals are “Predictable” for how many electrons they will lose: 1. Group 1A: will lose 1 electron (+1 charge) 2. Group 2A: will lose 2 electrons (+2 charge)

4. Oxidation-Reduction reactions Group 3A: mostly loses 3 electrons (+3 charge) Group 4A: “shares” electrons; involved in Type III compounds Group 5A: will accept 3 electrons (-3 charge) Group 6A: will accept 2 electrons (-2 charge) Group 7A: will accept 1 electron (-1 charge) Group 8A: noble gases; no loss or gain

5. Overall Equations Some chemical reactions will produce a product which will almost instantly undergo a 2 nd chemical reaction (decomposition) to form other products. An equation called an “over-all equation” combines both the initial double replacement reaction with the 2 nd decomposition reaction into one over-all equation.

6. Overall Equations It looks similar to a complete ionic reaction 1. The difference: a. it shows the reactants from both reactions combined together on the reactant side b. It shows the products from both reactions combined together on the product side

7. Overall equations Example: Cr 2 (SO 3 ) 3(aq) + H 2 SO 4(aq)  H 2 SO 3(aq) + Cr 2 (SO 4 ) 3(aq)  H 2 SO 3  SO 2(g) + H 2 O (L) 1. Step 1: Write all reactants and products of both reactions into one equation: Cr 2 (SO 3 ) 3(aq) + H 2 SO 4(aq) + H 2 SO 3  H 2 SO 3(aq) + Cr 2 (SO 4 ) 3(aq) + SO 2(g) + H 2 O (L) 2. Step 2: Remove substances on both sides of the equation that are not participating in the reaction (Here, remove H 2 SO 3 ), and re-write as an “overall equation”: Cr 2 (SO 3 ) 3(aq) + H 2 SO 4(aq)  Cr 2 (SO 4 ) 3(aq) + SO 2(g) + H 2 O (L)

8. Overall Equations 3.Step 3: re-write as a complete ionic equation 2Cr +3 (aq) + SO 3 -2 (aq) +2H + (aq) + SO 4 -2 (aq)  2Cr +3 (aq + 3S0 3 -2 (aq) + SO 2(g) + H 2 O (L) 4.Step 4: reduce to a net ionic equation 2H + (aq) + SO 4 -2 (aq)  SO 2(g) + H 2 O (L)