Chemical Bonds and Balancing Equations

1. Chemical Bonds and Balancing Equations EQ: Why do chemicals react? What is the difference between compounds, mixtures, and solutions?

2. Important Terms • Molecule- is two or more atoms combined and are physically attached. • Compound- is when two or more elements are combined by chemical bonds. • Usually found as a solid. • Ex. H2O = Water • Ex. NaCl = Sodium Chloride (Table Salt) • Solution- is when two or more substances are combined by dissolving a substance in pure water. • Usually found as a liquid. • Can be separated by boiling or distillation. • Ex. Salt Water; Sugar Water

3. Important Terms • Mixture- is when two or more substances are combined but ARE NOT chemically bonded. • Can be both solids and liquids. • Heterogeneous Mixture- Not an even mix throughout. • Ex. Fruit Salad, Pepper, Lucky Charms • Homogeneous Mixture - Even mix throughout. • Ex. Steel and Clear Salt Water

4. Recall • Why do elements react? • To achieve a more stable electron configuration (full outer shell)

5. What types of bonds are created? • Ionic - electrons are transferred from one element and give to another. • Metal joins with a Nonmetal STRONGEST CHEMICAL BOND • New terms • Cation-positive element • Anion-negative element • So sodium is a cation and chloride is the anion in NaCl(salt)

6. Covalent Bond • Atoms share electrons: NO ELECTRONS ARE SHIFTED OR REMOVED • Can create either single or double bonds to achieve full outer shell • Most Commonly done with gases that do not have a full outer shell (O2 Cl2 N2 ) • Atoms of the gases join up to achieve stability (weak bond, easily broken)

7. Understanding Chemical Reactions • Look at the following equation: • The reactants are to the left of the arrow • The products are to the right of the arrow • ReactantsProducts • Ag(NO3) + NaCl -------AgCl + Na(NO3)

8. Now list the number of atoms there are present for the Reactants and Products • Reactants • Ag • N • O • Na • Cl • Products • Ag • N • O • Na • Cl

9. Now write the number of atoms of each element • REACTANTS PRODUCTS • 1 Ag 1 Ag • 1 N 1 N • 3 O 3 O • 1 Na 1 Na • 1 Cl 1 Cl

10. Counting Atoms • Notice that ALL The atoms listed are EQUAL in number on BOTH SIDES of the reaction • In a chemical formula you assume the number 1 when no other number is listed

11. Counting Atoms • Notice that oxygen has 3 as its number! This is because oxygen is part of a polyatomic molecule. There are 3 oxygen atoms joined with the formula • Diatomic Molecule – “two” atoms combined to make a molecule. • Polyatomic Molecule – “three or more” atoms combined to make a molecule.

12. Now consider this formula • CH4 + O2 ----------------> CO2 + H2O • Reactants Products • C C • H H • O O

13. How many atoms are listed for the products and reactants Reactants Products C – 1 H – 2 O – 3 • C – 1 • H – 4 • O – 2 THIS CAN NOT HAPPEN! You must Balance the equation so that numbers of atoms for the reactants equal the same number for the products.

14. Balancing Equations • To do this we place coefficients (numbers) in front of the molecules in the formula to balance the atoms out • CH4 + O2 ----------------> CO2 + H2O • (Start with the atom with the highest number for either reactants or products) • It would be H in the example

15. Balancing Equations • Reactants Products • 1 C 1C • 4 H 2 H • 2 O 3 O • We need 2 more H in the products so we place a 2 in front of the water molecule • CH4 + O2 ----------------> CO2 + 2 H2O

16. Now Recheck • Reactants Products • 1 C 1C • 4 H 4 H • 2 O 4 O • Now we need to balance out the Oxygen in the Reactants. • CH4 + 2 O2 ----------------> CO2 + 2 H2O

17. Recheck • Reactants Products • 1 C 1C • 4 H 4 H • 4 O 4 O • It is now balanced!!!

18. Exit Slip • Balance this equation (its harder than it looks) • Al + O2 -----------> Al2O3