CHEMISTRY I
Ms. Wilson
Thornridge High School
Formulas and names
of
Ionic Compounds
Ions are particles with an electrical charge.
cations are positive
Na+
anions are negative
Cl-
MOLECULAR
COMPOUNDS
- H2O
- CO2
- C2H6O
IONIC
COMPOUNDS
- NaCl
- NaHCO3
- CaCl2
Composed of two or
more NONMETALS
Usually a METAL
and a
NONMETAL
-most are
crystalline solids at
room temperature
- gases or liquids at
room temperature
Predicting ion charge from the
Periodic Table
-Before writing formula for ionic compounds
you must learn how to predict the charge on ions.
-The charge on many ions can be predicted from
the Periodic Table.
-The charge on other ions can be
calculated.
There are 8 rules to learn
Metallic elements tend to lose electrons
and form cations. The ionic charge is
positive and numerically equal to the group
number.
This applies to elements in groups 1A, 2A,
and 3A:
1. Ions formed from elements in Group IA of
the periodic table have a 1+ charge.
Li+
Na+
K+
2. Ions formed from elements
in Group 2A of the periodic
table have a 2+ charge.
Mg 2+
Ca 2+
3. Elements in Group 3A
normally form ions with a
3+ charge. There are exceptions
but we will not discuss them here.
Aluminum is a common Group 3
metal.
It has a 3+ charge.
Al 3+
Nonmetals tend to gain electrons and
form anions. The charge is negative.
Groups 5A, 6A, and 7A have a
negative charge.
The charge is determined by
subtracting the group number
from 8.
4. Group 5A can form anions with a 3charge
example:
The nitride ion N3- reacts with a
metal to form
K3N
5. Group 6A can form ions with a 2- charge.
1. The Sulfide anion S 2reacts
with a metal to form
Na2S
examples:
2. The oxide anion O2reacts with metals to form
MgO
6. Group 7A elements
The Halogens form ions
with a charge of 1- .
They react with
metals
to form halides.
Example:
KBr
7. The majority of elements in
Group 4A and Group 8A
usually do not form ions.
- Carbon and Silicon the two nonmetals in
group 4A are ordinarily found in
molecular compounds.
- Carbon can however be + or - when forming
an ion.
- Group 8A elements rarely form compounds.
8. The algebraic sum of the
charges in the compound
is zero.
There should be an equal number
of cations and anions in the formula.
Back to 1st rule