Chem Lab Methods
Chemical Symbols

Use the chemical symbol for each element

Usually, the element abbreviations come
from the word
(He for Helium or Ti for Titanium)

Some elements have just one letter, such as
H for Hydrogen or N for Nitrogen




Most elements have two letters
Always capitalize the first letter and use
lower case on the second one.
Example: Cobalt is Co
If you used two capitals (CO), it would be
mistaken for Carbon Monoxide which has
one Carbon (C) and one Oxygen (O)
The subscript number specifies how many atoms
of that element you have

N2 is a nitrogen molecule with two atoms

C2H4 has two carbons and four hydrogens

CO2 contains one carbon and two oxygens

If no number is listed, it means there is only one
C2H3Cl
what elements and how many of each?

C2H3Cl
what elements and how many of each?

H2SiCl2
what elements and how many of each?

H2SiCl2
what elements and how many of each?

CH4
what elements and how many of each?

CH4 => methane
what elements and how many of each?



When there are large numbers in front, that
tells you how many molecules there are.
For example 3CH4 =

When there are large numbers in front, that
tells you how many molecules there are.
For example 3CH4 = 3 methane molecules

12NaOH = ?



When there are large numbers in front, that
tells you how many molecules there are.
For example 3CH4 = 3 methane molecules
12NaOH =
12 different
Sodium Hydroxide units


Counting Atoms
Nomenclature:
 Choosing of names for things
 Naming procedure
 Ionic Compound:
 Atoms held together by ionic bonds
 Binary Compound:
 Chemical compound made of atoms from
two different elements


Metal element name first

Then the non-metal element name,
but the ending is changed to -ide
Example: CaCl2 would be called calcium chloride
Example: Ag2O would be called…
silver oxide

Naming Binary Compounds
Example:
Compound name - Magnesium chloride
…What is the formula?
Magnesium Chloride =
Mg+2
What charge ion would each
atom form?
Cl-1
How many
of each to
make a
neutral
compound
?
 Magnesium Chloride:
Mg+2 and Cl-1
 The charge of the final compound must be neutral.
(The charges must balance)
▪ Need TWO Cl-1 ions to balance one Mg+2 ion
▪ (2 x -1) = (1 x +2) = 2 minus balances 2 plus
 (Criss Cross!)
 MgCl2
Mg1
Cl2
Magnesium Chloride = 1 Mg+2 + 2 Cl-1 => MgCl2
Mg+2
Cl-1
Example: Compound name Lithium sulfide
…What is the formula?
Lithium Sulfide=
Li+1
What charge ion would each
atom form?
S-2
How many
of each to
make a
neutral
compound
?
 Magnesium Chloride:
Li+1 and S-2
 The charge of the final compound must be neutral.
(The charges must balance)
▪ Need TWO Li+1 ions to balance one S-2 ion
▪ (2 x +1) = (1 x -2) = 2 minus balances 2 plus
 (Criss Cross!)
 Li 2 S
Li2
S1
Lithium sulfide = 2 Li+1 + 1 S-2 => Li2S
Li+1
S-2
Example: Compound name Aluminum oxide
…What is the formula?
Aluminum Oxide=
Al+3
What charge ion would each
atom form?
O-2
How many
of each to
make a
neutral
compound
?
 Aluminum Oxide:
Al+3 and O-2
 The charge of the final compound must be neutral.
(The charges must balance)
▪ Need TWO Al+3 ions to balance THREE O-2 ions
▪ (2 x +3) = (3 x -2) = 6 minus balances 6 plus
 (Criss Cross!)
 Al 2 O3
Al2
O3
Boron Oxide = 2 Al+3 + 3 O-2 => Al2O3
B+3
O-2
SUMMARY of approach:
 Determine what charge ion would form from
each element
 Decide how many of each charge are needed
to have a balanced (neutral) formula
OR do “Criss Cross”
 Write formula
 Subscripts state how many of each ion are needed
Ionic compound formula describes:
 One “unit” of the chemical compound
 Thus, it is called a “formula unit”
 Important definition

Example: 3 CaCl2
 Three “formula units” of calcium chloride

Writing (Balanced) Chemical Formulas
Two more details:

Complex ions: contain more than one element

Transition metals: ionic charges can vary

Examples:
 Acetate is (C2H3O2)-1
▪ Whole group has -1 ionic charge
 Carbonate is (CO3 )-2
▪ Whole group has -2 ionic charge

The ENTIRE group has one ionic charge

Acts like a single-atom ion of the same charge

List of common complex ions on the back of your
periodic table

All but ONE of the common complex ions are
negative
 Phosphate is (PO3)-3
▪ Whole group has -3 ionic charge
 Chlorate is (ClO3 )-1
▪ Whole group has -1 ionic charge

THE positive complex ion (worth memorizing) is:
 Ammonium (NH4)+1
 Magnesium Phosphate:
Mg+2 and (PO4)-3
 The charge of the final compound must be neutral.
(The charges must balance)
▪ Need THREE Mg+2 ions to balance TWO (PO4)-3 ions
▪ (3 x +2) = (2 x -3) = 6 minus balances 6 plus
 (Criss Cross!)
 Mg 3 (PO4)2
Mg3
(PO4) 2

Ionic charge can vary

How do you know?
 Listed on Periodic Table
 “Clue” in name
Element
Copper
Iron
Lead
Tin
Cation
Cu+
Cu2+
Fe2+
Fe3+
Pb2+
Pb4+
Sn2+
Sn4+
Name
Pronounced
Element
Copper
Iron
Lead
Tin
Cation
Cu+
Cu2+
Fe2+
Fe3+
Pb2+
Pb4+
Sn2+
Sn4+
Name
Copper (I)
Pronounced
copper one
Element
Copper
Iron
Lead
Tin
Cation
Cu+
Cu2+
Fe2+
Fe3+
Pb2+
Pb4+
Sn2+
Sn4+
Name
Copper (I)
Copper (II)
Pronounced
copper one
copper two
Element
Copper
Iron
Lead
Tin
Cation
Cu+
Cu2+
Fe2+
Fe3+
Pb2+
Pb4+
Sn2+
Sn4+
Name
Copper (I)
Copper (II)
Iron (II)
Iron (III)
Pronounced
copper one
copper two
iron two
iron three
Element
Copper
Iron
Lead
Tin
Cation
Cu+
Cu2+
Fe2+
Fe3+
Pb2+
Pb4+
Sn2+
Sn4+
Name
Copper (I)
Copper (II)
Iron (II)
Iron (III)
Lead (II)
Lead (IV)
Tin (II)
Tin (IV)
Pronounced
copper one
copper two
iron two
iron three
lead two
lead four
tin two
tin four
Write the chemical formula for Iron (II) Oxide

Step One: Determine the charges
 Iron (II) = Fe2+ and Oxide = O2-
Step Two: See how to balance the charges
Step Three: Find the combination that balances
Iron (II) Oxide = FeO
Write the chemical formula for Lead (II) Nitride

Step One: Determine the charges
 Lead (II) = Pb+2 and Nitride = N-3
Step Two: See how to balance the charges
Step Three: Find the combination that balances
Lead (II) Nitride = Pb3 N2

Do not use Roman Numerals for groups 1 or 2 as they are
always (+1) and (+2) accordingly.
K = +1
and Ca = +2
+1
+2

Do not use Roman numerals for transition metals that
always form the same charge ion.
 Ag = +1 and Zn = +2 and Cd = +2

Ionic Compound Formula Writing (all types)