WRAPPING UP CHEMISTRYWhatcha REALLY need to know…

Fall 2011

FROM CHAPTER 13…CHEMICAL BONDING Define Chemical Bonding… the

combining of atoms to form molecules or ionic compounds.

What is a Valence Electron? Electron found on the outermost shell of an atom and determines the element’s chemical properties (“hook-up” electrons)

How can I tell how many Valence Electrons an element has by looking at the Periodic Table? Group 1 has one; Group 2 has 2; Groups 3-12 vary (1-2); Group 13 has 3; Group 14 has 4…see a pattern??

MORE CHAPTER 13…

What are the “Magic Numbers” in dealing with Chemical Bonding? 2 (lower atomic #’s)or 8 (all the rest)

What groups are more likely to “hook up?”Group 1 and Group 17; Group 2 and Group 16…a pattern??

A LITTLE BIT MORE…

Define an Ionic Bond… bond that forms when electrons are transferred from one atom to another atom (give and take)

Positive Metals bond with Negative Nonmetals

Positive = lose Electrons (example Na+1)

Negative = gain Electrons (example Cl-

1) Negative = gain As long as the charges

balance out (-2 + +2) then it is neutral

WRAPPING UP 13… Define Covalent Bond… when atoms

SHARE one or more pairs of electrons Nonmetal/Nonmetal bond NOT Noble Gases…WHY?? They have a full

set of valence electrons (2 or 8) Most molecules are Covalent (O2 and N4) Metallic Bonds? Metal/Metal…loosely

bonded to allow for flexibility (malleability) – some are stronger than others

What is an alloy? Metals bonded together to strengthen properties Examples? Copper and tin = BRONZE; copper and zinc = BRASS; steel is an iron alloy

FROM CHAPTER 14: CHEMICAL REACTIONS…

How do you know you have witnessed a chemical reaction (chemical change)? A new substance is formed

What are some of the indicators? Gas formation; solid formation (PRECIPITATE); color change; energy change

Chemical bonds break during a chemical reaction, but develop new bonds during the process.

PARTS OF A FORMULA…

LEFT side = REACTANTSRIGHT side = PRODUCTARROW = “YIELDS”

COUNTING ATOMS…

How many atoms are in each formula? CH3COOH

CH3COCH3

NH4OH

C9H8O4

Ca(OH)2

CaO, (CaSO4)4

C6H12O6

LAW OF CONSERVATION OF ENERGY

Energy is NEVER created or destroyed; it is simply transferred during a chemical reaction

So, whatever energy you start with, you must also finish with

LAW OF CONSERVATION OF MASS/MATTER

Matter (mass) is NEVER created nor destroyed during a chemical reaction.

So, the number of atoms you finish with is ALWAYS the same number of atoms you started with

BALANCING EQUATIONS!

1.) Fe + O2 -> Fe2O3 

2.) KClO3 -> KCl + O2 

3.) Ca(OH)2 + H2SO4 -> HOH + CaSO4

4.) Cu + AgNO3 -> Cu(NO3)2 + Ag

5.) CrCl3 + NaOH--> Cr2O3 + HCl + NaCl

6.) NaClO3 --> NaCl + O2

TYPES OF CHEMICAL REACTIONS… 4 types… Synthesis – 2 substances combine to form a

new compound Example: 2 Na + Cl2 2NaCl

Decomposition – single compound breaks down into reactants (reverse of synthesis) Example: H2CO3 H2O + CO2

Single Displacement – one element or radical (compound) takes the place of another (they switch places) Example: Zn + 2HCl ZnCl2 +H2

Double Displacement – two elements or radicals (compounds) switch places in a reaction Example: NaCl + AgF NaF + AgCl

ENDOTHERMIC VS. EXOTHERMIC

Exothermic reaction – energy is released “exits” Can be written in an equation – ALWAYS on

the PRODUCT side Example: 2Na + Cl2 2NaCl +

energy Endothermic reaction – energy is taken

“in” Can be written in an equation – ALWAYS on

the REACTANT side Example: 2H2O + energy 2H2 +

O2

MANIPULATING REACTION RATES

The energy needed to start a chemical reaction is called: Activation Energy.

There are 5 ways you can manipulate reaction rates in a chemical reaction… Temperature Concentration Surface Area Inhibitors (only slow a reaction) Catalysts (only speed up a reaction)

FROM CHAPTER 15: CHEMICAL COMPOUNDS

How can you identify an ionic or covalent compound? Ionic – strong metal/nonmetal bond; brittle,

high melting points, soluble, electrical conductivity

Covalent – weaker nonmetal/nonmetal bond; low solubility, low melting points, most do not have electrical conductivity (except sugar)

ACIDS Indicator – a substance that changes

color in the presence of an acid or base What is an acid? Compound that

increases the hydronium ions (H3O+) when dissolved in waterWhat are its properties? Sour flavor,

corrosive, most are toxic, react with metals, turns litmus paper RED

How are acids used? Making paper, paint, detergents, fertilizers, rubber, plastics, citric acid (lemon, lime, orange juice)

BASES

What is a base? Compound that increases the number of hydroxide ions (OH-) What are its properties? Bitter

flavor, slippery feel, conduct electrical current, turns litmus paper BLUE

What are its properties? Soap, paper, oven cleaners, unclogging drains, cement, plaster, fertilizers, antacids

HOW WEAK OR STRONG? How do you know if an acid or base is weak or

strong? Use the pH scale of 1-14 How do you use the pH scale? Using litmus paper

and a color comparison chart; dip the litmus into the acid or base sample, compare the color of the litmus to the chart to see where your sample lies. Closer to 1 – STRONGER ACIDS Closer to 14 – STRONGER BASE 7 = NEUTRAL

Examples: Strong Acid = Lemon Juice (pH = 1) Weak Acid = Soft Drink (pH = 4) Strong Base = Ammonia (pH = 12) Weak Base = Ocean Water (8.5 pH) Neutral = Tap Water (6-8 pH) or Human Saliva (6.5-

7.5 pH)

FUSION OR FISSION

Nuclear Fusion – the combination of nuclei of small atoms to form a larger nucleus – energy is released

Nuclear Fission – splitting of nucleus of a large atom into two more fragments – energy and neutrons are released (atomic mass is manipulated)

Half-Life – time needed for half of a sample of a radioactive substance to undergo radioactive decay