Ionic Bonding
Definition of a Chemical Bond
The force that holds 2 atoms together.
WHY DO BONDS OCCUR?
 to seek the lowest possible energy state
 in most cases, combined atoms have a lower energy state than separate atoms.
IONIC BONDS:
 electrostatic force that holds oppositely charged particles together.
 e-s are TRANSFERRED to form charged particles
 most are METAL to NONMETAL combinations
So, when ionic compounds are formed:
1.
metals must lose all their outer electrons to form a positive ion - cations
2.
nonmetals must gain electrons until they are full to form a negative ion - anion,
which means they must have 8 electrons in the outer level. 8 electrons in the outer level is
known as the octet rule.
For example: Let's look at what happens when an ionic compound is formed from sodium and chlorine using
Lewis dot notation:
Na
Cl
= NaCl
Na
Na
= Na3N
You practice:
A.
sodium and nitrogen
Na
B.
N
strontium and fluorine
F
Sr
F
= SrF2
Properties of Ionic Compounds
The strong attraction of positive ions and negative ions in an ionic compound result in a crystal
lattice, which is a three-dimensional geometric arrangement of particles. In a crystal lattice, a positive ion is
surrounded by negative ions and vice versa. Because ionic bonds are relatively strong, the crystals that result
require a large amount of energy to be broken apart. Therefore ionic compounds have the following
properties:
 high melting points and boiling points
 conduct electricity in aqueous (aq) solutions (called electrolytes) in the molten state only, not as a
solid.
 ionic compounds are called SALTS
TERMINOLOGY
Formula Unit - a neutral compound formed between a cation and an anion and is the simplest ratio of the
ions represented in an ionic compound. Ex: LiBr
Monatomic ion - is a one-atom ion Ex: Ca +2
Oxidation number - is the charge of a monatomic ion and is equal to the number of electrons transferred
from or to an atom of the element to form the ion.
Ex: Ca loses 2 electrons & becomes +2, Cl gains 1 electron and becomes -1
Polyatomic ion – is made up of more than one atom and has an overall charge. Ex: (SO4)-2
Oxyanion - polyatomic ion composed of an element, usually a nonmetal, bonded to one or more oxygen
atoms. End in -ate or -ite where -ite has less oxygens than -ate.
Binary compound - made up of two ions/elements; the second ion/element ends in -ide. Two exceptions on
the ion list: Hydroxide (OH)-1and Cyanide (CN)-1
Ternary compound - made up of more than two atoms.
Superscript - a raised number that represents the oxidation number (charge) and IS NOT INCLUDED IN
THE FORMULA. Its purpose is to show our work in determining the subscript.
Ex: Ca +2
Oxidation number and O-3
Oxidation number
Subscript - a small number that represents the number of ions. If no subscript, then 1 is understood.
Ex: H2O shows: 2 hydrogen atoms and 1 oxygen atom
Rules for Writing Formula given the name
1. METAL ION IS ALWAYS WRITTEN 1ST
 -write the symbol of the metal with its oxidation # as a superscript
 -If it’s a transition metal (groups 3-12) the oxidation # must be given by a Roman Numeral and
it is the oxidation number. If the Roman Numeral is not given, then look at the top of the ion list.
 If more than one atom (usually in parenthesis) then the name and oxidation # is on the
polyatomic list.
2. NONMETAL ION IS ALWAYS WRITTEN 2ND
 -If it ends in “ide” writ the symbol and its oxidation # from the Periodic Table.
 -If it ends in “ite” or “ate” look on the Polyatomic Ion sheet for the symbols and oxidation #.
 Note the substitutions at the bottom of the page for Halogens**
3. Crisscross the oxidations numbers only (not the charges +/-) to become the subscripts and write the
formula. (if the oxidations numbers are equal but opposite in charge-making it neutral, then you can
erase the charges)
For instance:
1.
Sodium chloride
Na
3.
+1
Cl = NaCl
tin (II) sulfide
Sn
+2
S
2.
-1
-2
= SnS
silver fluoride
Ag
4.
+1
F -1 = AgF
calcium oxalate
Ca +2 (C2O4) -2 = Ca(C2O4)
For instance:
1.
magnesium bromide
+2
Mg Br
3.
-1
= MgBr2
zinc fluoride
Zn
+2
-1
F
= ZnF2
2. copper (II) nitride
Cu +2 N -3 = Cu3N2
4. ammonium carbonate
(NH4)+1 (CO3)-2 = (NH4)2(CO3)
5.
lead (IV) sulfate
Pb+4 (SO4)-2 = Pb2(SO4)4 = Pb(SO4)2
***If subscripts can be reduced, then you must do so!
Rules for writing the name when given the formula
1. Metal Ion
 If monatomic, find the symbol of the metal ion on the periodic table and write the name down
exactly.
 If a transition metal without a constant charge, then you must determine the Roman Numeral.
To determine the Roman Numeral, go backward in the crisscross steps. If there are no
subscripts, then the metal ion charge is = to the nonmetal ion charge. (If subscripts, then 99% of
the time, reverse the crisscrossing works. The only time it doesn’t is if the compound was
reduced – in which you can then check the nonmetal ion charge.)
Nonmetal Ion


If monatomic, find the symbol of the nonmetal ion on the periodic table. You must change the
ending of the name to “ide. For example: Chlorine becomes Chloride.
If polyatomic, find the name of the ion list and write it down.
For instance:
1.
Li3N
Lithium Nitride
2. (NH4)2S
Ammonium Sulfide
3.
RaAt2
Radium Astatide
4. CuCl2
Copper II Chloride
5.
PbO
Lead II Oxide
(no subscripts so check the nonmetal and Oxygen is -2 so it must have been reduce)
Pb+2O-2
ACIDS
Acids are a group of compounds that are given special treatment in naming.
Acids are compounds that give off hydrogen ions when dissolved in water.
There are two types of Acids:
Binary Acids
The formula of acids in the form HX, where is Hydrogen and X is a monatomic anion. We have previously
named the compound HCl, hydrogen chloride. When the compound HCl is dissolved in water, it is named as
an acid.
Ternary Acids
The formula of acids in the form HX, where is Hydrogen and X is a polyatomic anion. For example HNO3,
exist only in water solution. They are always named as acids.
Rules for Naming Acids:
The acid can be named using three rules that focus on the ending of the anion of the acid (See Table).
1. For Binary Acids: When the anion (X) ends in –ide, the acid name begins with the prefix hydro-. Then the
stem of the anion has the suffix –ic and it is followed by the word acid. Thus HCl (X = chloride), dissolved in
water, is named hydrochloric acid. H2S (X = sulfide) is hydrosulfuric acid.
2. For Ternary Acids: When the anion ends in –ite, the acid name is the stem of the anion with the suffix –
ous, followed by the word acid. H2SO3 (X = sulfite) is sulfurous acid.
3. For Ternary Acids: If the anion ends in –ate, the acid name is the stem of the anion with the suffix –ic,
followed by the word acid. Thus HNO3 (X = nitrate) is nitric acid.
Table - Naming Acids
Type
Binary
Anion Ending
-ide
Ternary
-ite
Ternary
-ate
1
2
3
Example
HCl
Cl1- Chloride
H2SO3
SO32- sulfite
HNO3
NO31- nitrate
Example
Naming these compounds as acids. a. HClO
Solution
a. hypochlorous acid (rule 2)
b. HCN
Acid Name
Hydro-(stem)-ic acid
Example
Hydrochloric acid
(stem)-ous acid
Sulfurous acid
(stem)-ic acid
Nitric acid
c. H3PO4
b. hydrocyanic acid (rule 1)
c. phosphoric acid (rule 3)
Writing Formulas of Acids:
Formulas of acids are most easily written by using the preceding three rules in a reverse fashion.
Hydrobromic acid (hydro- prefix and –ic suffix), according to rule 1, must be a combination of hydrogen ion
and bromide ion (Br-). The formula of hydrobromic acid is HBr.
Hydrogen ion and phosphite ion (PO33-) must be the components of phosphorus acid (rule 2). The formula of
phosphorous acid is H3PO3.
What is the formula of chloric acid? As rule 3 shows, chloric acid (-ic ending) must be a combination of
hydrogen ion (H+) and chlorate ion (ClO3-). The formula of chloric acid is HClO3.
Practice:
1. Name these compounds as acids.
a. HF
c. H2SO4
b. HC2H3O2
d. HNO2
2. Write formulas for the following acids.
a. chromic acid
b. hydroiodic acid
c. chlorous acid
d. perchloric acid