Chemical Bonds and
Balancing Equations
EQ: Why do chemicals react?
What is the difference between
compounds, mixtures, and solutions?
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 (NaCl,
Sugar..ect) and is a solid
 Solution- is when two or more elements
are combined by chemical bonds and are
in a liquid state. (every drop is the same
concentration HCL, Vinegar)

Important Terms
Mixture- is when two or more elements are
combined but ARE NOT chemically
bonded (liquid or solid)
 Heterogeneous mixture- Not an even mix
throughout, (chocolate milk, salt and
pepper, Italian salad dressing)
 Homogeneous mixture- Even mix
throughout (milk, sand, and smoke)

Recall
Why do elements react?
 To achieve a more stable electron
configuration (full outer shell)

What types of bonds are
created?
Ionic-electrons are transferred from one
element and give to another:
STRONGEST CHEMICAL BOND
 New terms
 Cation-positive element
 Anion-negative element
 So sodium is a cation and chloride is the
anion in NaCl(salt)

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)

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

Reactants
Products
 Ag(NO3) + NaCl ------- AgCl + Na(NO3)

Now list elements in both the
reactants and products
MAKE SURE ALL ARE LISTED
Reactants
 Ag
N
O
 Na
 Cl

Products
Ag
N
O
Na
Cl
Now write the number of atoms
of each element






REACTANTS
1 Ag
1N
3 O
1 Na
1 Cl
PRODUCTS
1 Ag
1N
3 O
1 Na
1 Cl
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


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
Now consider this formula





CH4 + O2 ----------------> CO2 + H2O
Reactants
C
H
O
Products
C
H
O
How many atoms are listed for
the products and reactants





Reactants
Products
1C
1C
4H
2H
2O
3O
THIS CAN NOT HAPPEN! You must Balance the
equation so that numbers of atoms for the reactants
equal the same number for the Products
To do this we place 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







Reactants
Products
1C
1C
4H
2H
2O
3O
We need 2 more H in the products so we place a 2 in front of
the water molecule
CH4 + O2 ----------------> CO2 + 2 H2O
Now Recheck






Reactants
Products
1C
1C
4H
4H
2O
4O
Now we need to balance out the Oxygen in the
Reactants.
CH4 + 2 O2 ----------------> CO2 + 2 H2O
Recheck

Reactants
1C
4H

4O



It is now balanced!!!
Products
1C
4H
4O
Homework

Balance this equation (its harder than it
looks)
 Al
+ O2 -----------> Al2O3