Chapter 7
7.2: Ionic Bonds & Ionic
Compounds
The Formation of Ionic Bonds
 Objectives
 Describe
the formation of ionic bonds and
the structure of ionic compounds.
 Generalize about the strength of ionic
bonds based on the physical properties of
ionic compounds.
 Categorize the formation of an ionic bond
as exothermic or endothermic.
The Formation of Ionic Bonds
 A positively charged cation is attracted
to a negatively charged anion.
 The electrostatic force of attraction
holding oppositely charged particles
together is called an IONIC BOND.
Ionic Compound
 Defined as a compound having an ionic
bond
 It is a compound that is composed
entirely of ions yet has a “0” overall
charge.
Ionic Compounds
A
binary ionic compound contains only 2
different elements – a metal cation and a
nonmetal anion (ex. NaCl)
Forming Ionic bonds
 Even though they contain charged particles,
ionic compounds are electrically neutral.
the number of electrons
lost by a cation must equal the
number of electrons gained by the
anion.
 This means,
 The electrical charges of the cations and
anions must balance (the total of all the
charges has to add up to zero).
Example: NaCl
See Table 4, p. 211
Na
Cl
+
[Na]
[ Cl
]
NaCl
Showing ionic compound formation
using electron dot structures
The Formation of Ionic Bonds
 Consider the formation of the ionic
compound, calcium fluoride, using electron
configurations.
 Calcium is a group 2A metal: [Ar] 4s2


How many electrons will calcium lose to gain a
noble gas configuration?
What is its charge?
 Fluorine is a group 7A nonmetal: [He] 2s22p5
 How many electrons will fluorine gain to attain a
noble gas configuration?
 What is its charge?
The Formation of Ionic Bonds
 The number of electrons lost must equal the
number of electrons gained; the total of the
charges must add to zero.


The # of electrons lost does not equal the # gained.
The total of the charges does not equal 0 (+2 + -1 =
+1).
 Therefore, another F ion is needed –
each F will gain 1 electron, for a total of
two. That means, the # of electrons lost
will equal the # gained; the total of the
charges will be 0.
The Formation of Ionic Bonds
 One Ca+2 will form an ionic bond with
two F-.
 The formula for the compound will be
CaF2 – the subscript of 2 below F
means there are 2 F- in the compound.
 The name of the compound will be a
combination of the names of the 2 ions
that make it up - calcium fluoride.
 Practice worksheet
Properties of Ionic Compounds
 The cation & anion have a regular,
repeating pattern; forming an ionic
crystal
 There is no such thing as 1 unit of NaCl
– Large numbers of ions are found
together in a crystal, in a ratio that
balances the charges.
 For example, in NaCl, cations and
anions are in a 1:1 ratio
Ionic Compounds
Ionic Compounds
 The formula, NaCl, is an empirical
formula – through the subscripts, it
gives the smallest possible ratio of ions
– 1 Na+ to 1 Cl This ratio is determined by the number
of electrons transferred in ionic bonding
Ionic Crystals
 Each type of crystal has a characteristic
shape.
NaCl
Calcium carbonate
Ionic crystal
 The 3-d geometric arrangement of
particles is called a crystal lattice.
 Ionic compounds have different crystal
lattice structures because they have
differently charged ions making up that
structure.
Properties of Ionic Compounds
 Melting points, boiling points, and hardness
depend on the strength of the attraction
between the ions in the compound. They are
generally high numbers.
Properties of Ionic Compounds
 Dissolve readily in water because they
dissociate: NaCl --> Na+(aq)+ Cl-(aq)
 In a solid, ions are locked into position and
electrons cannot flow freely—solid ions are
poor conductors of electricity.
 Ionic compounds, in a liquid state or in
aqueous solution, are good conductors of
electricity since electrons can move freely.
 Ions in aqueous solution that conduct
electricity are called electrolytes.
Properties of Ionic Compounds
 Ionic crystals are hard, yet they are
brittle.
 This figure demonstrates how and why
crystals break when an external force is
applied.
The Formation of Ionic Bonds
 During any chemical reaction, energy is
either absorbed or released.
 If energy is released, the reaction is
exothermic.
The Formation of Ionic Bonds
 The formation of ionic compounds from
positive and negative ions is almost
always exothermic.
 The attraction of the positive ion for the
negative ion forms a more stable
system that is lower in energy than the
individual ions.
The Formation of Ionic Bonds
 The energy required to separate one
mole* of ions in an ionic compound is
referred to as the lattice energy.
 The more negative the lattice energy,
the stronger the force of attraction, the
harder to separate the ions.
 * I mole = 6.02 x 1023 ions
Trends in Lattice Energy
 In smaller ions, the ions are closer in
space and require a greater lattice
energy to separate. See NaF vs. NaI in
Table 6, p. 217
 Compounds of ions with larger ionic
charges will have greater lattice energy.
Compare NaCl and SrCl2