Chemistry Lesson: Balancing Equations and Molecular Models

1. Bell work – place in the top margin of page ____: Name the following compounds: • MgO • LiBr • NO7 Find the name of these polyatomic ions (page 27). • PO4 3- • OH-

2. Balancing Chemical Equations October ___&_____

3. Agenda: • Notes • Lab Activity • Independent Practice • Exit Slip at the end

4. Law of Conservation of Mass • Law of Conservation of Mass: States that mass is neither created nor destroyed in any ordinary chemical reaction

5. 2. When a chemical reaction takes place, it always follow this format: Reactants  Products • Reactants= your starting stuff; always located before the arrow • Arrow ()= yield (means the reaction took place) • Products= the end result; always after the arrow

6. Check For Understanding • Cl2 + 3F2 2ClF3 • What are the products? • What are the reactants?

7. Check For Understanding • H2+ O2 2H2O • Products? • Reactants?

8. Subscripts and Coefficients • An uppercase letter next to a lower case letter represents ONE element; example: Na (sodium) • If there is not a number behind the element you can say you have one atom of that element; Example: CO2:you have 1 carbon atom.

9. Subscripts and ( ) • When a number is “little” and BEHIND an element, we call that a subscript • When there are parentheses around a compound & and a subscript outside, the subscript multiplies EVERYTHING in the ( ). Example: (PO)4 would mean P=4 and O=4

10. Guided Practice Example: NaClNa =_____ Cl =_____ The next examples you are trying with a partner- 2 mins • H2O H=_____ O=_____ • C8H10N4 C=_____ H=_____ N=_____ • Ca(CN)2Ca=____ C=______ N=_____ • (SO4)4S=______ O=______

11. Subscripts and Coefficients e. Coefficient: A number YOU can place in front of a compound to change how much you have of elements within that compound *Example: 4NaCl What is the Coefficient? How many Na atoms do we have now? How many Cl atoms do we have now?

12. Guided Practice: Coefficients AND Subscripts With a partner try the following: • 4Ag2O Ag=______ O=_______ • 25H2OH=_______ O=_______ • 2Ca3(PO4)2 Ca=______ P=_______ O=_______ • 16CO2C=______ O=_______

13. Lab Activity • Before we continue with balancing, we are going to do an activity for about 10 minutes using jelly beans and toothpicks to build our own molecule models • The purpose of this activity is to give you a change to tangibly see what the difference is for example between 2H2O and H4O2 • Like normal I will show you how to setup your notebook

14. 5. Balancing Equations • Always make a T- chart to count up your reactants and your products • Know that if an equation is unbalanced, you MAY NOT CHANGE THE SUBSCRIPT. You are only allowed to change the coefficient out in front • If you do not put a coefficient in front of a compound, we treat it as a 1 • Count how many atoms you have for each element BEFORE you start placing coefficients out in front

15. Example • ____ Hg + _____ Br2 _____ Hg2Br2 • Make a chart to make sure everything is balanced! • Is this balanced/follow the Law of Conservation of Mass? • Why or why not?

16. Example • _____H2 + O2 _____H2O • Make a chart to make sure everything is balanced! • Is this balanced/follow the Law of Conservation of Mass? • Why or why not?

17. Example (#7) • ____Cl2 + ____F2 ClF3 • Make a T-chart, and make sure each side is balanced!

18. Independent Practice • Continue to do the rest of the problems on the practice sheet. • Glue in on page 29 when you are done!