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
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 ChargesMonatomic ionsIons 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 chargeThe 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 Atoms that
commonly form
ions
Charge on
ions
1 H, Li, Na, K, Rb, Cs 1+
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-
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 compoundsIt 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 elementsThey 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 SO4
2- 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