1. Balancing Equations and mols

2. Some Rules... Remember...when elements are in a chemical reaction, they form a new substance Example: Sodium and Chlorine react to form Salt (Sodium Chloride) RULE ONE: In a compound name, The cation (positive charge) is written before the anion (negative charge) Example: NaCl because Na+ and Cl-

3. You Try rule one

4. atoms vs molecules RULE TWO: when we have the smallest amount of an element that can still maintain all of the element’s properties we call that an ________________? When we have the smallest amount of a compound that can still maintain all of the compound’s properties we call that a _____________?

5. You try rule two

6. How many Atoms? When we write atoms and molecules out there are often numbers that come before and after in the formulas. Rule 3: If the number comes after (is to the right) of an element name and is subscript, it is the number of atoms of that element (if no number there is one atom): Ex: H2 has two atoms of H or H-H Ex: H has one atom of H Ex: H2O has two atoms of H and one atom of O

7. Number of molecules If a compound is bracketed, the number that follows refers to the number of molecules of that compound. Ex: (SO 4 ) 6 has 6 molecules of SO 4 This means there are 6 atoms of S and 6 x 4 atoms of O (24 atoms of O). Ex: H2(CO2)2 has 2 atoms of H and 2 molecules of CO2 2 molecules of CO2 have 2 atoms of C and 2 x 2 atoms of O (4 atoms of O).

8. You Try Rule Three

9. The numbers in Front Rule 4: The numbers that come before the names of elements and compounds in chemical equations refer to the number of atoms or molecules that are written after the number These are the ONLY numbers that can be changed to balance equations!!!!! Ex: 4H2O means 4 molecules of H2O (8 H and 4 O total) Ex: 2H2SO4 + 4CO2 means 2 molecules of H2SO4 and 4 molecules of CO2 How many total H, S, O in 2H2SO4?

10. You try Rule 4...

11. Balancing Equations We write out chemical reactions in equations with the reactants(what you start with) on the left side and products(what you end up with) on the right side Ex: Sodium and Chlorine react to form Sodium Chloride Na + Cl2 NaCl PROBLEM: we started with two atoms of Cl but ended with only one!

12. Balancing Equations We must fix our problem by changing the numbers of reactants and/or products to balance WE CANNOT END UP WITH MORE OR LESS ATOMS THEN WE STARTED WITH! For Na + Cl2 NaCl we must add a 2 to the front of Na and a 2 to the front of NaCl 2 Na + Cl 2 NaCl Now it is balanced

13. Try with this way H2 + O2 H2O H HHHHOOOO OO HHHH ç√ OOOO HHHH HHHH HH OO HHHH OO HH 2 H2 + O2 = 2H2O

14. You Practice Balancing Equations