Ionic Bonds

An ionic compound is composed of positive
and negative ions that are combined so that the
numbers of positive and negative charges are
equal. (neutral net charge)

Ionic Bonding occurs between a
metal and a nonmetal element,
and has an electronegativity
difference greater than 1.7.

✔

The nonmetal has a higher
electronegativity than the metal.

✔

The valence electrons of the metal are
transferred to the nonmetal.

✔

The number of electrons gained or lost
will be equal to the number of electrons
needed to form a stable octet of 8
electrons.

fluorine ion

F^-1

lithium ion

Li⁺¹

Most ionic compounds exist as a
crystalline solid.

Crystalline Solid:

a three dimensional network of

positive and negative ions
mutually attracted to one

another.

This orderly, three dimensional arrangement
of ions is called a crystal lattice.

Atoms form bonds to
reduce potential energy,
and increase stability!

The amount of energy given off by the formation of
one mole of an ionic crystalline compound is known
as the compound’s lattice energy.

A compound’s lattice
energy indicates the
strength of the ionic

bonds.

The chemical formula for an ionic
compound, called a formula unit, is
the ratio of ions present in the
crystalline structure.

The simplest whole number
ratio of ions = a Formula
Unit of the compound.

✔ High melting point
✔ High boiling point

Therefore, most ionic compounds
are a solid at room temperature.

✔

Conductors of electricity in the molten state (melted) or
dissolved (in solution)

In the solid state, ionic compounds will not conduct electricity.
When it’s melted or dissolved, ions are free and can conduct
electricity.

Salt, NaCl, dissolving in water.

Write the dot diagrams for:
Na
Mg
Al
Si
Cl
Ar
He

Electron Dot

Diagrams

Mg

Na

Al

Si

Cl

Ar

He

Step 1: Count the number of valence electrons to be
accounted for in the structure.

Step 2: Draw the skeletal structure with the central atom. Show
shared pairs of electrons by using a — (dash) instead of dots.

NH4

+1

The central atom will be the atom with the
least electronegativity or carbon if present.

N

H H

H

H

Electrons: 5 + (4)1 – 1 = 8 e-

Hydrogen will never be the central
atom—it can only form one bond.
If more than one carbon is present,
they will be attached in the center.

N

H

H

H

H

✔

Define ionic compound.

metal to nonmetal or polyatomic ion

✔

Formation of an ion.

cations & anions

✔

Formation of an ionic compound

✔

Crystal lattice structure

lattice energy (higher = stronger bond)

Properties of Ionic Compounds (due to crystal lattice structure)

✔

high boiling point

✔

high melting point—mostly solids at room temp.

✔

brittle

✔

conductors of electricity only in molten state or in solution—not
as a solid.