Counting Atoms and
Balancing Chemical Equations
Write what is in Blue
Elements, Compounds,
Mixtures




Hydrogen is an element.
Oxygen is an element.
When hydrogen and
oxygen bond they make the
compound water.
When salt and water are
combined, a mixture is
created. Compounds in
mixtures retain their
individual properties.
The ocean is a
mixture.
Elements, compounds, and
mixtures



Mixtures can be separated by physical means.
Compounds can only be separated by chemical
means.
Elements are pure substances. When the
subatomic particles of an element are separated
from its atom, it no longer retains the properties
of that element.
Identifying Compounds
Each new element is identified by a capital
letter
 Example: H2SO4


The elements in Sulfuric Acid
 Hydrogen
 Sulfur
 Oxygen
Subscripts

C12H22O11
There are 12 atoms of Carbon
 There are 22 atoms of Hydrogen
 There are 11 atoms of Oxygen

If there is not a subscript listed, it is
understood to be 1.
 Example: NaCl

There is one atom of Sodium
 There is one atom of Chlorine

You Practice!
NaHCO3
HCl
Sodium – 1
Hydrogen – 1
Carbon – 1
Oxygen -3
Hydrogen – 1
Chlorine - 1
There are times you will see a compound
with parenthesis.
Pb(NO3)2
The 2 after the parenthesis indicates there
are two sets of the parenthesis.
Pb(NO3) (NO3)
So, in counting the atoms, you would have
the following:
Lead – 1
Oxygen - 6
Nitrogen -2
You Practice!!
(NH4)3PO4
Mg(OH)2
Nitrogen – 3
Hydrogen – 12
Phosphorus – 1
Oxygen – 4
Magnesium – 1
Oxygen – 2
Hydrogen – 2
Coefficient
2H2SO4
This means there are 2 compounds of
Sulfuric Acid. Think:
H2SO4
H2SO4
Counting the atoms:
Hydrogen – 4
Sulfur – 2
Oxygen - 8
You Practice!!
3H3PO4
2H2O
Hydrogen – 9
Phosphorus – 3
Oxygen - 12
Hydrogen – 4
Oxygen - 2
Got It????
Chemical Equations
Chemical equations express what is
happening in a chemical reaction using
symbols.
4K + Cl2
Reactant
2KCl
Product
Law of Conservation of Mass
In a chemical reaction, matter
cannot be created or
destroyed. It can only be
changed.
What does that mean??
The reactants MUST contain the
same elements and the same
number of each element as the
product. They CAN be in different
compounds.
HUH?????
H2 + O2
Reactants: H = 2
Products: H = 2
H2O
O=2
O=1
This cannot happen. An oxygen atom
cannot be destroyed.
So what do we do?
The chemical equation must be written
according to the law.
AGAIN --- HUH???
H 2 + O2
H2O is the production of
water. Well, how it actually happens in
nature is this….
2H2 + O2
2H2O
Reactants: H = 4 O = 2
Products: H = 4 O = 2
Do I Need to Know How to
Balance?
NOT YET. You need to be able to recognize
if the chemical reaction follows the law of
conservation of mass.
Na + O2
Mg + 2HCl
Na2O NOPE
MgCl2 + H2 YUP!!
You Practice!!!
HgO
N2 + 3H2
Zn + 2HCl
Hg + O2
NOPE
2NH3
YUP
ZnCl2 + H2
YUP
More Practice
K + Br2
2KBr
2Fe + O2
6Fe2O3
2Na + 2H2O
NOPE
NOPE
2NaOH + H2
YUP
Got It???
Warm Up 3/9
Is it balanced? Show your work!!

Al + O2 ---> Al2O3

SiCl4 + H2O ---> H4SiO4 + HCl
Balancing Chemical Equations
H2 + O2
Reactants: H = 2
O=2
H2O
Products: H = 2
O=1
What do we multiply by 1 to get 2?
Keep Going….
H2 + O2
Reactants:
2H2O
Products:
2=H = 4
2 =O = 2
Now the Oxygen is balanced but Hydrogen is not,
so what do we multiply by 2 to get 4?
Almost There!!!
2H2 + O2
2H2O
Reactants:
Products:
4 H=4
2=O = 2
Now it is balanced!!! Congratulations, you
have now learned the hardest thing we will
do all year!!
Now You Practice
HgO
Hg + O2
=Hg =
=O =
K + Br2
2KBr
=K =
=Br =
Warm Up 3/11
Write Q&A

Why do we have to balance equations?
(What law do we have to follow?)
Warm Up 3/10
Write Q&A

Balance the Following:

HNO3 + Ca(OH)2  Ca(NO3)2 + H2O
Warm Up 3/8
Write the Following:
The Law of Conservation of Mass
In a chemical reaction, matter
cannot be created or
destroyed. It can only be
changed.
Warm Up 3/5
Write Q&A

How many atoms are in 3Pb(OH)4?
Pb
O
H

Warm Up March 4
Write Q&A

The vertical columns on the periodic table
are called ______________ and they
correspond to the number of __________

The horizontal rows on the periodic table
are called ____________ and they
correspond to the number of __________