Chemical Symbols and
Formulas
Chapter 2.7
Chemical Symbols
All elements in the Periodic Table have
symbols that are recognized world wide.
 It does not matter which country you
are in or the language you speak.
 Example: The element Iron is always
identified by “Fe” and Oxygen is “O”.
 The names are not always the same but
the symbols are. “Fe” is iron in Canada,
fer in France and fier in Romania.

Chemical Symbols
A Chemical symbol is
an abbreviation of a
name of an element.
Element
Oxygen
Chemical
Symbol
O
Capital letter if only
one letter.
Only first letter
capital if more than
one letter
Nitrogen
N
Hydrogen
H
Sodium
Na
Sodium comes from the word sodanum, a
headache remedy, and it’s symbol (Na)
comes from the Latin word Natrium.
Chemical Formulas
A chemical formula is the combination of
symbols that represent a particular
compound.
The chemical formula indicates which
elements are present in the compound
and in what proportions.
Ex. 1: Water molecule
H2O: 2 atoms of hydrogen, 1 atom of oxygen
Ex. 2: Iron Oxide molecule
Fe2O3: 2 atoms of iron, 3 atom of oxygen
Chemical Formulas - Examples




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Calcium Carbonate (chalk) – CaCO3
Sodium Chloride (salt) – NaCl
Acetysalicylic acid (aspirin) – C9H4O8
Acetic acid (vinegar) – C2H4O2
Chemical Formulas
NOTES:
- Each symbol in a formula represents an
element.
- If only one atom of an element is present in
the compound, no subscript is used.
- If more than one atom of an element is used,
then the symbol is followed by a number
indicating how many atoms are used. This is
called the subscript.

Homework
Do Questions #1–5 on Page 59
 You may use your Periodic Table.
 Make sure that for each question
you write out that question first then
you write your answer and then
continue on to the next question and
so on until completed.

1 atom of sodium
2 atoms of hydrogen (in a hydrogen molecule)
3 atoms of magnesium
2 atoms of phosphorus
8 atoms of oxygen
3 carbon atoms
13 total atoms
Tomorrow
Go over counting atoms worksheet
Pass in Homework
Chapter 2 quiz