1. Unit 2-Chemical Bonds & Solution Chemistry Textbook Ch.6-9 (p.174-323)

2. Why are atoms compared to Legos?
They can combine in different ways to form different compounds and molecules.

3. Chemical Bonds
Chemical Bond – the force that holds atoms or ions together in a compound
In a reaction, bonds are broken and rearranged

4. Chemical Structure
Chemical Structure – the arrangement of atoms in a substance
Structure determines properties
e.g., state of matter, melting and boiling
points

5. Compounds & Molecules
Compound – A substance made up of atoms of 2 or more different elements joined by chemical bonds
Molecule – A group of atoms that are held together by chemical forces
e.g., Water is a compound because it is made up of two different elements (H and O) and a single molecule of water contains 2 hydrogen atoms and 1 oxygen atom (H2O)

6. Why do bonds form?
Atoms join to form bonds so that each atom has a stable electron configuration (full outer level).

7. Types of Bonds
Ionic Bond – The attractive force between oppositely charged ions

8. Types of Bonds
Covalent Bond – A bond formed when atoms share one or more pairs of electrons

9. Types of Bonds Differences Between Ionic & Covalent Bonds
Ionic Compounds
Covalent Compounds
Structure
network of bonded ions
molecules
Valence Electrons
transferred
shared
Electrical Conductivity
good (when melted or dissolved)
poor
State at Room Temperature
solid
solid, liquid, or gas
Melting & Boiling Points
generally high
generally low
Usually between
metals / nonmetals
nonmetals

10. Types of Bonds
Metallic Bond – A bond formed by the attraction between positively charged ions and the electrons around them.

11. Polyatomic Ions Polyatomic Ion – An ion made of two or more atoms
Parenthesis group the atoms

12. TEXTBOOK SECTION ASSIGNMENT:
Read {6.1 & 6.2 p
Complete p.182 Q’s 1, 3-5 and p.190 Q’s 1, 3, 5, 6, 7, 9

13. Chemical Reactions
Physical Change -A change that alters the form of a substance but not the chemical makeup of the substance, a change of state
Words like: crush, smash, tear, evaporate, slice, dissolve, absorb, swell, burst

14. Chemical Reactions
Chemical Change - One or more substances combine or decompose to form a chemically different substance
Words like: react, burns, forms, decomposed, rusting, sours, rotting, digesting, cooked, molecular change
Another word for a chemical change is a chemical reaction

15. Chemical Reactions
Chemical reactions occur when chemical bonds are formed or broken
Strong chemical bonds resist change: glass
Weak chemical bonds breakdown easily: wood
Why do chemical reactions occur?
Atoms become more stable when they bond.

16. Chemical Reactions
Chemical reactions produce new substances that can usually be detected by observing the evidence:
Color change
Precipitation
Temperature change
Property change
Gas produced

17. Structure of a Chemical Equation
Law of Conservation of Mass - Matter cannot be created nor destroyed so there must be the same number of atoms on each side of the equation
Beginning materials are reactants
Ending materials are products

18. Structure of a Chemical Equation
Coefficient – a whole number in front of an element or molecule in a chemical reaction
Tells how many of each element or molecule is present

19. Structure of a Chemical Equation
Be careful!!!
Do not confuse coefficients with subscripts!

20. Structure of a Chemical Equation
Remember...
Chemical formulas show the ratio of elements found in molecules and compounds
Subscripts:
If no subscript present it is assumed to be 1 atom
If elements in brackets or parenthesis, treat same as in math.

21. Structure of a Chemical Equation
Coefficients:
Coefficients multiply the entire molecule’s atoms
CaCl2
Ca=1
Cl=2
Ca3(PO4)2
Ca=3
P=2
O=8
2Ca3(PO4)2
Ca=6
P=4
O=16

22. Structure of a Chemical Equation
To satisfy the Law of COM, you must add all reactant molecules together & compare with all molecules in the products
The # of reactant atoms must equal the # of product atoms

23. Energy & Chemical Reactions
Chemical reactions can be categorized by the way energy flows into and out of the process

24. Energy & Chemical Reactions
Exothermic Reactions: Heat is RELEASED.
Products will have less potential energy than reactants.
Examples: Burning wood in a fire makes smoke and ash that has less stored energy than the wood. It releases heat and light energy
Reactants  Products + Energy

25. Energy & Chemical Reactions
Endothermic Reactions: Heat is ABSORBED.
Thermal energy gets stored in the chemical bonds – the products will have more potential energy than the reactants.
Examples: Frying an egg; decomposing H2O; instant cold packs
Reactants + Energy  Products

26. Classifying Reactions
There are millions of possible reactions
...however, there are only a few general kinds of reactions
Patterns can be used to identify kinds of chemical reactions and to predict products of these reactions

27. Synthesis Reaction
Definition: Reaction in which two or more substances combine to form a new compound
General Form:
A + B  AB
Example:
2 Na + Cl2  2NaCl

28. Decomposition Reaction
Definition: Reaction in which a single compound breaks down to form two or more simpler substances
General Form:
AB  A + B
Example:
2H2O  2H2 + O2

29. Single-Displacement Reaction
Definition: Reaction in which one element takes the place of another element in a compound
In general, the more reactive element will take the place of the less reactive one
General Form:
AX + B  A + BX
Example:
3CuCl Al  2AlCl Cu

30. Double-Displacement Reaction
Definition: Reaction in which a gas, a solid precipitate, or a molecular compound forms from the apparent exchange of atoms (or ions) between two compounds
General Form:
AX + BY  AY + BX
Example:
Pb(NO3)2 + K2CrO4  PbCrO4 + 2KNO3

31. Combustion Reaction
Definition: The oxidation reaction of an organic compound in which heat is released.
Oxygen is always a reactant
organic compound – contains carbon
Example:
CH4 + O2  CO H2O

32. Oxidation-Reduction (“REDOX”) Reaction
Definition: Any chemical change in which one species is oxidized (loses electrons) and the other species is reduced (gains electrons)
Example:
4Fe O2  2Fe2O3
**Each Fe loses 3 electrons to form Fe+3 ions while each O2 gains 2 electrons to form O2- ions

33. Rates of Reaction
Reaction Rate: how fast a chemical reaction takes place
Collision Theory: Rate of the reaction depends on the frequency of the collisions between atoms
Anything that increases the contact between particles increases reaction rate. (Anything that decreases contact slows the rate.)

34. Factors Affecting Reaction Rate
There are six major factors that affect the number of collisions of particles in a reaction.
Concentration
Surface area
Temperature
Pressure
Molecular size
Catalysts

35. Factors Affecting Reaction Rate
Concentration – the greater the concentration of reactants, the faster the reaction rate
Example: Using a concentrated bleach will bleach clothes faster than a diluted bleach

36. Factors Affecting Reaction Rate
Surface Area – the more surface area in contact between the reactants, the more atoms can interact, so the faster the reaction goes
Example: Sawdust burns faster than a log

37. Factors Affecting Reaction Rate
Temperature– the higher the temperature, the faster the atoms are moving, the more collisions they have, making the reaction occur at a faster rate
Example: Rusting of iron happens faster at a higher temperature

38. Factors Affecting Reaction Rate
Pressure–Putting reactants under higher pressure will force more atoms together harder….so the reaction rate will increase.
Example: The piston in your car compresses the gas-air mixture before it burns.

39. Factors Affecting Reaction Rate
Molecular Size-Big molecules are slower, they have fewer collisions, and therefore they react slower.
Example: Sugar burns slower than hydrogen

40. Factors Affecting Reaction Rate
Catalysts-Substances that do not enter into the chemical reaction but encourage collisions.
Example: Catalytic converters-catalysts of platinum, palladium, and rhodium in cars; Enzymes-proteins in the body
“Reverse catalysts” (inhibitors)-Substances that slow down reactions

41. TEXTBOOK SECTION ASSIGNMENT:
This assignment will be checked next class:
Read {7.1, 7.2 & 7.4 p , p in textbook
Complete the following practice problems
p.224 Q’s 1-5
p.229 Q’s 1-3
p.247 Q’s 1-3, p.253 Q 19