Ionic Bonding
Ionic Bonding
Occurs when electrons are transferred from one atom
to another, forming two ions
The ions stay together because of electrostatic
attractions (btw positive & negative atoms)
Ionic bonds form easily between alkali metals and
halogens
The Octet Rule
Atoms tend to gain, share, or lose electrons in order
to obtain a full set of valence electrons (in most cases
this equals 8)
An octet of electrons consists of full s and p sublevels on
an atom.
Exceptions: transition elements and rare earth elements
Example
Na + Cl
+
Na +
Cl
-
Properties of Ionic Compounds
 Ionic compounds do not
form molecules; they form a
crystal lattice
 The green spheres are Na+
and the red spheres are Cl -
This is a crystal of
CaCl2. Each ion is
held rigidly in
place by strong
electrostatic
forces that bond it
to several
oppositely
charged ions
Other Properties
Normally form between metals and nonmetals
Ionic compounds have ions that form very strong bonds,
which makes them hard and brittle
They have high melting points and high boiling points
When dissolved in water, the solution will conduct
electricity
Types of Ions
There are two types of ions
Monatomic: cation or anion that consists of a single atom.
Examples: Na+ and ClPolyatomic: two or more atoms that act as a single ion (or
particle). Examples: (CO3)2- and (OH)-
Types of Ionic Compounds
Ionic compounds will be a combination of
a metal and a nonmetal (if the cation is
monatomic)
There are two types of ionic compounds
Binary Ionic Compounds: contains the ions of
only two elements (NaCl, CaCl2)
Polyatomic Ionic Compounds: contain at least
one polyatomic ion (CaCO3, Mg(OH)2)
The names DO NOT indicate the ratio of
ions present, but the formulas do
Names of Charged Particles
When electrons are lost, the ion has an overall positive
charge and is called a cation Examples: Na+, Ca2+
When electrons are gained, the ion has an overall
negative charge and is called an anion Examples: F-, S2The negative ions will attract the positive ions and form a
bond
All ionic compounds are electrically neutral
Ionic Charges
Monatomic ions
Ions that consist of only one atom
Charges often can be determined by using the
periodic table
Many of the transition metals have more than
one charge
The charge on the ion is indicated by using a Roman
numeral next to the name of the element
• Cu has a 1+ and a 2+ charge. Cu 1+ is called Copper I,
and Cu2+ is called Copper II
A few transition metals have only one charge
The names of these do not have to include a Roman
numeral
• Zn, Cd
Monatomic Ions
Group
Charge on
ions
1
Atoms that
commonly form
ions
H, Li, Na, K, Rb, Cs
2
Be, Mg, Ca, Sr, Ba
2+
13
B, Al
3+
15
N, P, As
3-
16
O, S, Se, Te
2-
17
F, Cl, Br, I
1-
1+
Ionic Compounds
Writing formulas for binary ionic
compounds
Compounds composed of two elements are
called binary compounds
When the formula is written, the charge of the
cation must be balanced by the charge of the
anion
The overall charge of the ion combination must be
zero
The cation is always written first in the formula
Writing Formulas for Ionic Compounds
 To write the formula for an ionic compound:
Write the chemical symbol and overall charge of the
cation or polyatomic cation: Na+, Ca2+, NH4+
Write the chemical symbol and overall charge of the
anion or polyatomic anion: Cl-, O2-, NO3Add the charges
If equal, write the chemical symbols together,
e.g. NaCl, CaO, NH4NO3
If not equal, crisscross values of the charges
and make them subscripts, e.g. Ca(NO3)2,
CaCl2
Crisscross Method (also called “Drop and Swap”
Na+ can combine with S2The value of the charge on Na, which is 1, becomes the subscript
for S: S
The value of the charge on S, which is 2, becomes the subscript
for Na: Na2
The resulting formula is Na2S
Naming Ionic Compounds
Naming binary ionic compounds
It is important to know the Stock naming system
and the charges on cations before naming ionic
compounds
The process is the reverse of writing formulas
Polyatomic ionic compounds
Compounds that contain atoms of three different elements
They usually contain a polyatomic ion; must be recognized first to be able
to name the compound correctly
Tightly bound groups of atoms that behave as a unit and carry a charge
Have the suffix –ite and –ate
• These ions will be given to you on a sheet; you will not have to memorize them
• Hydroxide and cyanide are the only common polyatomic ions that end in –ide
Common Polyatomic Ions
Ion
Name
Ion
Name
NH4+
Ammonium
NO2-
Nitrite
NO3-
Nitrate
OH-
Hydroxide
CO32-
Carbonate
SO42-
Sulfate
O22-
Peroxide
C2H3O2-
Acetate
SO32-
Sulfite
ClO3-
Chlorate
You will get these on a chart for tests and quizzes!!
How Do I Write the Formulas for
Polyatomic Ions?
Put parentheses around any polyatomic
ion and add subscripts to the outside of
the parentheses.
Never change the subscript of a
polyatomic ion (it will change the
composition of the ion):
Ca(OH)2, Ca3(PO4)2
Include the subscript inside the parentheses
Practice
Sodium combines with fluorine
Chlorine combines with hydrogen
The nitrite ion combines with calcium
The ammonium ion combines with nitrogen