Notes:Color Guide• Gold: Important concept. Write this down.

• Orange: Definition. Write this down.

• Blue: Important information, but you do not need to copy.

• Red: Example. Copy if needed.

• White: General Discussion (Don’t Copy)

Chapter 6: Chemical ReactionsSection 1: Forming Compounds

• Definition: chemical reaction – the process that causes a substance to change into a new substance.– Chemical reactions cause atoms to REARRANGE.

– One example of a chemical reaction occurs when cations join with anions.

Chemical Reaction

Ionic compounds form when cations and anions bond together.

• When ionic compounds form, the new compound must have no charge.

In other words, all of the + and - charges must cancel out.

Neutral!

Charged Charged

Each cation and anion has it’s own charge. Lets look at the cations first. Please copy into your notes.

Use only the element symbols.Group 1

1+ ChargeGroup 2

2+ ChargeGroup 133+ Charge

Lithium: Li1+ Beryllium: Be2+ Aluminum: Al3+

Sodium: Na1+ Magnesium: Mg2+

Potassium: K1+ Calcium: Ca2+

Rubidium: Rb1+ Strontium: Sr2+

Cesium: Cs1+ Barium: Ba2+

Francium: Fr1+ Radium: Ra2+

And now for the anions:• When a nonmetal becomes an anion, it’s name changes.

– Example: Fluorine Fluoride– Example: Oxygen Oxide

Group 171- Charge

Group 162- Charge

Group 153- Charge

Fluoride: F1- Oxide: O2- Nitride: N3-

Chloride: Cl1- Sulfide: S2- Phosphide: P3-

Bromide: Br1- Selenium: Se2-

Iodide: I1-

Astatine: At1-

In order to form the new compound, the anions and cations must cancel each other’s charg.

What happens if the charges DON’T cancel out???

• To make Sodium Oxide, there must be enough Sodium Cations to balance the Oxygen Anion.

Na1+ O2-

Na1+

Na2O1

Why don’t we add another sodium cation to the reaction?

It took 2 Sodium

to balance the 1 Oxide.

• Lets try another one. How about Magnesium Chloride?

• This stuff is actually pretty easy…

Mg2+ Cl1-

Cl1-

Mg1Cl2

It took 2 Chloride to balance the 1 Magnesium.

Try these on your own:•Aluminum BromideAlBr3

•Calcium NitrideCa3N2

One more thing to remember…the metal always comes first. It keeps its original name.

The nonmetal comes second. It changes it’s name.

Easy!

• Covalent compounds are named based on the number of atoms they contain.– Prefixes are used to represent the number of atoms.The Prefixes Are:

1 Mono2 Di3 Tri4 Tetra5 Penta6 Hexa7 Hepta8 Octa

Rules: •If the first element has only one atom, it gets no prefix.•The first element uses it’s original name.

Examples:

• Carbon Di-oxide

• Di-Hydrogen Di-oxide

• Sulfur Tetra-Chloride

Chapter 6: Chemical ReactionsSection 2: The Nature of Chemical Reactions

There are often signs that a chemical reaction is taking place:

– Color Change– Gas Production (bubbling)– Energy Transfer (getting hot or cold, glowing)

– These signs indicate that something is being changed & new substances are forming.

So, in a chemical reaction…things REACT to PRODUCE other things.

• Definition: reactants – the substances in a chemical reaction that are changed.

• Definition: products - the NEW substances produced in a chemical reaction.

– The product must contain the same elements as the reactant.

During a chemical reaction, atoms are rearranged.

C8H18 O2 H2O CO2+ +

Carbon Hydrogen Oxygen

Hydrogen Carbon Oxygen

Lets look at the reaction of gasoline and oxygen again…

– It would be far to dangerous to use gasoline as a fuel if it immediately reacted with oxygen, right?

– What do we need in order to start the reaction?

A SPARK!

• Some chemical reactions need energy in order to begin.

– Energy breaks the atomic bonds and allows the atoms to rearrange.

– Once the bonds are broken, the reactants rearrange into the products.

BAM!

Perhaps the most important rule in chemistry is:

• Definition: Law of Conservation of Mass – states that “In a chemical reaction, mass is never created or destroyed.”

– In other words, you MUST have the same number of atoms in the reactant as you have in the product.

Some reactions release energy as they occur…– Definition: exothermic change – a physical

or chemical change that releases energy.•Exo. changes make the air warmer or give off

light (or both).•Examples: combustion and condensation

Some reactions absorb energy as they occur…–Definition: endothermic change – a

physical or chemical change that absorbs energy.•Endo reactions lower the temp.•Examples: evaporation

Chapter 6: Chemical Reactions

Section 3: Types of Reactions

• Definition: chemical equation – a representation of a chemical reaction using element symbols.– The means “yields” or “produces”.

Chemical reactions are classified based on what happens to the reactants.

Some reactions break the reactants apart…Others causes them to join together.Others just make them change places.

• When things combine together in a chemical reaction, we call it “synthesis”.

• Definition: synthesis reaction – a reaction in which two or more substances combine.

• The general formula is:–A + B AB

• A and B represent the reactants…• AB represents the product.

When a chemical reaction breaks substances apart, it is called “decomposition”.

• Definition: decomposition reaction – a reaction in which a compound breaks down into simpler substances.

The general formula is:

AB A+B

• AB represents the reactant.• A + B represent the products.

In replacement reactions, substances change places.

• Definition: single replacement reaction – a reaction in which one element takes place of another to form a new compound.

–The general formula is: –AX + B BX + A

– Definition: Double Replacement reaction – a reaction in which two elements trade places.

–The general formula is: –AX + BY AY + BX

Notice that X takes the place of Y and Y takes the place of X.

• Definition: combustion reaction – an exothermic reaction in which oxygen is (usually) a reactant.– Combustion reactions often produce H2O and CO2 as

products.