Ionic Compounds
Summary
Ionic bonding occurs from the transfer of electrons from one atom to another. Ionic bonds
require an electron donor and an electron acceptor. The electron donor is typically a metal,
which transfers its electrons and forms a positively charged ion (cation). The electron acceptor
is typically a nonmetal, which accepts the metal's electrons to form a negatively charged ion
(anion).
Thus, an ionic bond is composed
of cations (typically metals) and
anions (typically non metals)
that sum up to a net charge of 0.
Na
Everyday Ionic Compounds
Ionic compounds are formed from ionic bonds that hold
them together. Check out the ionic compounds that you
probably use every day!
NaF
KI
NaHCO3
Ingredient in toothpaste, added to
water supplies to promote healthy teeth
Table salt
If your salt label reads "iodized table salt,"
it contains KI. Promotes healthy thyroid
function.
Otherwise known as "baking soda."
Used for all purpose cooking and cleaning.
Properties of Ionic Compounds
Form a crystal lattice structure due to strong
attraction between cations and anions
High melting and boiling points due to crystal
lattice structure
Form strong electrolytes in water (conduct
electricity)
Opposite charges cause the compounds to be polar
Dissolve easily in water (because water is also
polar)
Hard and brittle as a solid
Act as good insulators when in solid state
Designed by Rachel Beckham
Cl
Cl1-
Na1+
-
+
+
+
-
-
-
+
+
+
+
-
+
+
+
-
-
-
-
-
+
+
+
-
Ionic compounds are composed of
cations and anions. These
oppositely charged ions form a
crystal lattice structure to optimize
their attractionto one another. This
results in a highly stable compound
when in its solid form. When
immersed in water, this crystal
lattice structure breaks apart, and
the ions separate.
Did you know?
The melting point of NaCl (table salt)
is 1,472 F! Why? Because the cations
and anions form a strong crystal
lattice structure, which increases the
bond strength, which increases the
amount of energy to break apart their
crystal lattice structure!
Ionic Compounds
How to Name
Ionic compounds are named in the following fashion:
Name of cation (metal) + Name of anion (nonmetal), but remove ending and change to "-ide"
Ex: Sr3N2
Nitrogen
Strontium
Nitride
As shown above, the cation (the metal) is named first, followed by the anion (the nonmetal).
The cation's name is not changed in any way, but the anion's name ending is replaced with
"-ide". This replacing of the name ending always occurs for anions. For example, O 2- is an
oxygen atom, but it is referred to as "oxide" because it is in its anion state.
How to Name Transition Metals
Ionic compounds that contain cations with varying charges must include the charge of that
cation using roman numerals in parenthesis. Because most transition metals have varying
charges, roman numeral typically must be added. This means that you will have to identify
the charge that the cation must have for the net charge to be 0!
For example, write the name of FeO.
Since Fe is a transition metal, we need to find out the charge of Fe for this compound.
We know that:
(number of Fe atoms) (charge of Fe) + (number of O atoms) (charge of O) = 0
Nitrogen's charge is -3. (If you don't know this, go back to the charges of families and
memorize!). When we plug this in along with the number of Fe and N atoms, we get:
(1)(x) + (1)(-2) = 0
x = +2
When we solve for x, we see that Fe = +3.
Therefore, the name of FeO will be iron (II) oxide.
Let's try naming Cu2(CO3)3!
(2)(x) + (3)(-2) = 0
x = +3
When we solve for x, we see that Cu = +3. Thus, the name of Cu2(CO3)3 will be copper (III) oxide.
You Try It!
1. Name the following substances:
a. MgCl2
b. NiBr2
c. Fe2O3
Designed by Rachel Beckham
d. Al2O3
Ionic Compounds
Writing Formulas
Writing formulas for ionic compounds is simple! The total positive charge must equal the total
negative charge so that the net charge is zero. For example, consider lithium and chlorine.
Lithium has 1 valence electron and will donate its outer electron to form a +1 charge, or Li 1+.
Chlorine has 7 valence electrons and will accept lithium's extra electron to form a -1 charge, or
Cl1-. One lithium ion and one chlorine ion will result in a net charge of 0. Thus, the resulting
formula is LiCl. Now consider an ionic compound between Mg and Cl. Mg will donate its two
outer electrons to form a Mg2+ charge. Cl will form a Cl1- ion. In order to have a net charge of 0,
we will need two chloride ions and one magnesium ion. The resulting formula will therefore be
MgCl2. Note that the subscript "2" indicates the number of chloride ions present in that
compound.
*Note: In order to write formulas for ionic compounds, you must know the specific
charges of each group on the periodic table. If you don't, go back and review!
The Cross Over Rule
Write symbols
and charges
Mg2+ Cl1Al3+ P3Be2+ Se2Ga3+ CO32-
Cross over charges
=
=
=
=
MgCl2
Al3P3
Be2Se2
Ga2(CO3)3
=
=
=
=
Reduce
Confirm net charge = 0
MgCl2
+2 + [2(-1)] = 0
AlP
1(+3) + 1(-3) = 0
BeSe
1(+2) + 1(-2) = 0
Ga2(CO3)3
2(+3) + 3(-2) = 0
✓
✓
✓
✓
* Note: NEVER change the subscripts on polyatomic ions. Make sure to put
parenthesis around the polyatomic ion before crossing over the charge!
1.
Write out the
symbols and
charges of the
atoms
2.
cross over the
magnitudes (remove
the + or - sign)
of the charges.
3. reduce to the
4.
simplest ratio of
ions if needed
Do the math to
confirm that the
net charge is zero
You Try It!
1. An unknown compound is tested and found to
have a low melting point and does not dissolve
readily in water. Based on this information, is
this substance an ionic compound?
2. Which of the following substances are ionic
compounds?
MgS, Be3(PO4)2 ,H2SO4, H2O, CH4, Rb2O, CF4
Designed by Rachel Beckham
3. Write formulas for the following
compounds:
a. Sodium fluoride
b. Rubidium hydroxide
c. Calcium nitrate
d. Copper (II) chloride
e. Iron (III) nitrate