Grade 10 Science –Chemistry
Ionic Compounds
Science Perspectives 10 - Section 5.6 Pages 192-195
Compound
 A Pure Substance composed of two or more elements in a FIXED RATIO
Ionic Compound
 A compound made up of one or more positive metal ions (cations) and one or more
negative non-metal ions (anions)
Ionic Bond
 The simultaneous strong attraction of positive and negative ions in an ionic compound.
As noted, ionic bonding occurs between metals and non-metals. Yet, “why and how” does this
type of bonding occur?
Figure 1 shows the element Neon. Neon is a NOBLE GAS found in
Group 18. As such, its outer shell (VALENCE) has the maximum number
of electrons (i.e., the outer shell is full). Thus, the electron configuration is
STABLE. In other words, Noble Gases are not reactive.
Figure 1. Bohr-Rutherford Diagram
for Neon (Element #10)
Figure 2 is the element Nitrogen. Its outer shell is NOT full. Thus, the
electron configuration is UNSTABLE. To become stable (i.e., have an
outer shell with the maximum number of electrons), nitrogen will either
GIVE AWAY or TAKE electrons from another element. When this
happens, the NITROGEN ION is formed.
In an IONIC BOND, an ion with a positive charge (cation)
will give away electrons while an ion with a negative charge
(anion) will take electrons.
Figure 2. Bohr-Rutherford Diagram
for Nitrogen (Element #7)
WHY?
 In every ionic bond, the cation typically has a small ionization energy (i.e., it has a “small
amount of energy” to hold its electrons) while the anion has a large electron affinity (i.e., it
has a “large amount of energy” to attract electrons). When the two elements are close
together, the affinity exceeds the ionization energy, the electron “moves” from the cation
to the anion, and an ionic compound “linking” the two ions is formed.
 In a stable state (i.e., a full outer shell or a full VALENCE OCTET of electrons) , the
energy state is at its lowest. This is preferred. This is stability. Elements seek to be at
this low energy state. Breaking the ionization energy hold or seeking electrons through
affinity raises the energy state of the element to a higher level. This is not preferred
because it represents an unstable state. If the element can add or remove electrons, it
gets to a lower energy state and stability.
In ionic bonding, the metal gives its outer electrons to the
non-metal. Electrons are transferred in this type of bonding.
The metal has lost electrons, and is now a positive ion or
cation. The non-metal has gained electrons, and is now a
negative ion or anion. As the ions have opposite charges, they
will attract each other. This attractive or electrostatic force is
called an ionic bond. Figure 3 shows an ionic bond.
Can you identify the cation and the anion in Figure
3? Explain your answer.
Figure 3. Ionic Bond showing
movement of electron between sodium
and chlorine
It is important to understand that the bond is a FIXED
RATIO (see Page 193 in your textbook). When sodium
bonds with chlorine, there is always one sodium for one
chlorine and sodium chloride (table salt) forms. Thus, the
ratio is 1:1. We do not see this ratio; rather, we see table
salt as a small white fragment. Under a microscope,
sodium chloride looks like a cube (see Figure 4). It
contains billions of alternating sodium and chlorine ions.
Look closely – there is always one sodium ion for every
one chlorine ion. In this bond, the ratio is 1:1.
NOTE: The ration is NOT always 1:1. Rather, the ratio
Figure 4. Sodium chloride crystal
depends on the number electrons to give away or
take to reach a stable state (see Figure 5 on Page 193).
Water Solubility
Solubility is the ability to dissolve in water. For example, salt dissolves in water. When a
compound dissolves, the ions separate. Water molecules (H2O) surround each ion and prevent
the ions from bonding again (see Page 193).
QUICK QUESTION: What is the FIXED RATIO of water? What does that mean?
Properties of Ionic Compounds
Ionic bonds are strong. Thus, most ionic compounds have the following properties:
 Hard, brittle solids
 High melting points
 Dissolve in water to form ELECTROLYTES (i.e., solution that conducts electricity)
QUICK QUESTION: Distilled water is a poor conductor of electricity. On the other hand, lake
water or water in a swimming pool is a good conductor of electricity. Why?
Covalent Bonds
Covalent bonds are formed as a result
of the sharing of one or more pairs of
bonding electrons. Each atom
donates half of the electrons to be
shared. This sharing of electrons is as
a result of the electronegativity
(electron attracting ability) of the two
bonded atoms are either equal OR the
difference is no greater than 1.7. If the
electronegativity difference is greater
than 1.7, the higher electronegative
atom has an electron attracting ability
large enough to force the transfer of
electrons from the less electronegative
atom. This would be an ionic bond. As
long as the electronegativity difference
is no greater than 1.7 the atoms can
only share the bonding electrons.
Figure 5. Diagram illustrating Covalent and Ionic Bonds
A chemical bond formed by sharing a pair of electrons
iscalled a COVALENT BOND. The diatomic hydrogen
molecule (H2) is the simplest model of a covalent
bond. The shared pair of electrons provides each
hydrogen atom with two electrons in its valence shell
orbital.
NOTE: For the nonmetals AND the 's' block metals, the number of valence electrons is equal to
the group number.
Element
Group
Valence Electrons
Bonds needed to form valence octet
F
7A
7
1
O
6A
6
2
N
5A
5
3
C
4A
4
4
There are many covalent bonds with hydrogen (hydride compounds) including water.
HOMEWORK
Page 195 – Questions 1-10, 12