Unit 3 Review

This PowerPoint follows along with the Unit 3 Review Worksheet

Protons Neutrons Electrons

• Atomic number = # Protons

• Atomic number = # Electrons– Unless there is a charge

• Atomic mass - # protons = # neutrons

Reminder: Oxidation State is the same thing as Charge

39K+1

ChargeMass

Principle Energy Levels

• The electron clouds are found at specific distances from the nucleus called Principle Energy Levels

• Elements in the same row of the periodic table have the same number of occupied energy levels

Periods = Rows = Principle Energy Levels

Valence Electrons

• The electrons that occupy the highest energy level (or the outer shell) are called Valence Electrons

• Elements in the same column of the Periodic Table have the same number of valence electrons and have similar chemical properties.

SKIP!Groups = Columns = Valence Electrons

Ions

• Atoms that have either lost or gained electrons are called ionsions.

• Ions that GAIN electrons have a NEGATIVE charge and are called anions.

• Ions that LOSE electrons have a POSITIVE Charge and are called cations.

Has a “t” that looks like a “+” sign!

Gain or Lose ?• Atoms will gain or lose electron in order to

obtain a full outter shell. This means they may lose electrons to empty the last shell, or gain electrons to fill the last shell (with 8 electrons, except for Hydrogen and Helium)– Lithium only has 1 valence electron so it would

rather lose 1 than gain 7. This means it will have a charge of +1.

– Fluorine has 7 valence electrons so it would rather gain 1 than lose 7. This means that it will have a charge of -1.

Oxidation vs Reduction• Elements in columns 1-13 tend to undergo

Oxidation (lose electrons) and form Positive ions. These are metal elements

• Elements in columns 15-17 tend to undergo Reduction (gain electrons) and form Negative ions. These are non-metal elements

Oxidation ReductionIs IsLoss Gain

Lithium Loses an Electron

Li Li+1 + 1 e-

Electron is being lost Electron is being lost resulting in a positive chargeresulting in a positive charge

LiLi LiLi+1+1

Fluorine gains an electron

F + 1 e- F-1

Fluorine gains an electrons Fluorine gains an electrons resulting in a negative chargeresulting in a negative charge

FF-1-1FF

Lithium Fluoride

When lithium loses When lithium loses and electron, it will and electron, it will give it to fluorine give it to fluorine

resulting in an ionic resulting in an ionic bondbond

Types of Chemical Reactions

• Synthesis

• Decomposition

• Single Replacement• Double Replacement

• Dissociation

• Combustion

+

++ +

+ +

++ charge

- charge

Hydrocarbon + O2 CO2 + H2O

Criss Cross Method

• Mg+2 + P-3

Mg3P2

• 3(+2) + 2(-3) = 0

Take the absolute value of the charges and

switch the value with the other element to obtain

the subscript value

Naming Compounds

• Positive Metal Name + Negative Non-Metal Name (change ending to “ide”)

• Example:• Na2O

• sodium oxide

Note that the subscripts do NOT have any affect on

the name

Moles…

• H3PO4 contains 98 grams per 1 moles If you have a container with 343 grams of H3PO4 , how many moles does it contain?

H = 1 gram per mole x 3 = 3 grams

P = 31 grams per mole x 1 = 31 grams

O = 16 grams per mole x 4 = 64 grams

Total = 98 grams

Calculating molar mass

molar mass

343 grams = 3.5 moles

Dimensional Analysis

Ratio / Cross Multiplying

98 grams = 1 mole

343 grams = X moles

1 (343) 98 X=

1(343) = 98X 98 98

X = 3.5 moles

1 mole98 grams( )molar mass

Calculating percent by mass…• The percent by mass of an element in a compound can be

determined:% by mass of element = total mass of element in compound X 100

total mass of the compound

Example: Calculate the percent composition of magnesium in MgF2.

Mg mass = 24.3MgF2 mass = 24.3 + 19 + 19 = 62.3

So... 24.3 x 100 = 39 % 62.3

• When a bond is broken energy is required.

• When a bond is made energy is released.

Reactants ProductsENDOTHERMIC

EXOTHERMIC

• Particles speed up when heat is added, this process is considered endothermic because heat is absorbed.

• Particles slow down when heat is removed, this process is considered exothermic because heat is lost

HEAT

HEAT

Tem

p.

Melting H +endothermic

Boiling H +endothermic

Freezing H –exothermic

Condensing H –exothermic

Time heat added

Balancing Reactions

• Because of the law of conservation of mass, reactions must have the same amount of atoms in their reactants as they do in their products.

• The atoms can be rearranged into different compounds, but there must be the same amount.

+ +

SC + T CT2 + S

THIS IS NOT BALANCED!

2

The coefficients balance out the equation

Subscript indicates bondingCoefficient indicates how many

Click here to get more practice with Balancing Reactions