Chemical Formula
matter
atom
molecule
element
O
O2
compound
ex: H20, NaCl
symbol - p 20
•usually 1 or 2 letters
that are used to identify
an element
•only 1st letter is
capitalized (ex: He helium)
symbol
hydrogen
H
Co
CO
Co - cobalt
CO - carbon, oxygen
formula - p 20
• a combination of symbols
that shows the ratio of
elements in a compound
• Ex: H2O, the ratio of
Hydrogen to Oxygen is 2:1
formula
Example (add to notes on formula)
• CH4 (methane)
• 1:4 ratio
• 1 Carbon atom: 4 Hydrogen atoms
Word Equations
A word equation gives the names of the
substances involved in a reaction. For example:
copper + oxygen
→
copper oxide
Copper and oxygen are the reactants, and copper
oxide is the product.
Chemical Equations
Chemical equations give the symbols and
molecular formula of the substances involved in a
reaction. In the example below, if we just replace
the words shown below with the correct chemical
formula, we will get an unbalanced equation, as
shown here:
copper + oxide yields copper oxide
Cu + O2 →
CuO
Chemical equations give the symbols and molecular
formula of the substances involved in a reaction. In the
example below, if we just replace the words with the
correct chemical formula, we will get an unbalanced
equation, as shown here:
Copper + oxygen yields copper oxide
Cu + O2 → CuO
To make things equal, we need to adjust the number
of units of some of the substances until we get equal
numbers of each type of atom on both sides of the
arrow.
Here is the balanced chemical equation:
2Cu + O2
→
2CuO
2Cu + O2  2CuO
atoms
two
Elements
compounds
fewer
larger
three
three
10
21
more than a billion
b
c
e
a
d
2
2
sulfur
1
oxygen
2
nitrogen
hydrogen
1
3
3
4
3
3
3
3
2
hydrogen
carbon
oxygen
carbon
hydrogen
oxygen
magnesium
2
1
3
12
22
11
1
1
sulfur
oxygen
sodium
oxygen
hydrogen
hydrogen
4
1
6
45
6
3
1
1
2
oxygen
2
4
2
4
iron
oxygen
sodium
hydrogen
carbon
oxygen
2
5
3
1
1
1
3
6