Ionic Bonding

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Ionic Bonding

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Chemical Bonds

There are three basic types of chemical bonds:

With Ionic Bonds,the electrostatic attraction between ions
forms ionic compounds.

With Covalent Bonds, valence electrons are shared
between atoms to form either network solids or molecules.

With Metallic Bonds,the valence electrons of many metal
atoms are shared to form a "sea" of electrons within a
metallic solid.

In this unit, we will be studying ionic bonds.

Electronegativity is a measure of how strongly an atom attracts
electrons.

Atoms with a higher electronegativity tend to attract electrons
away from atoms with lower electronegativity.

This removal of electrons can occur when the difference in
electronegativity between the two atoms is about 1.7 or higher.

Once a positive and negative ion are formed, they will be
attracted to each other via the electrostatic force:

Ionic Bonding

r2
F = k q1 q2

Ionic Bonding

Both these atoms are electrically neutral, they have no charge.

The atom on the left has 1 valence electron and the atom on
the right has 7.

They would both have full outer shells if the single valence
electron on the left was taken by the atom on the right.

The atom on the right is more electronegative, so it takes the
single valence electron making both atoms more stable.

Ionic Bonding

r2

k q1 q2
F =

Cation

q = +1

Anion

q = -1

After taking that valence electron, the atom on the left has become
a cation with a charge of +1 while the atom on the right has become
an anion with a charge of -1.

There is now an electrical attraction between them due to their
opposite charges.

Ionic Bonding

The ions are now bonded together by a very strong electrical force.

This electrical force is the ionic bond that holds the ions together.

Remember, the electron that was captured by the anion is not
shared; it is bound to the anion.

The cation and anion are attracted to each other by electrical force.

Cation

q = +1

Anion

q = -1

r2

k q1 q2
F =

Ionic Bonding

Atoms with higher electronegativity attract valence electrons from
atoms with lower electronegativity.

An electronegativity difference of at least 1.7 is needed for the
formation of ions.

Which pairs of elements will have that great a difference in
electronegativity?

+ Cation

- Anion

An electronegativity difference of 1.7 or more can only occur
between a metal and a nonmetal.

Ionic Bonding

Na

Cl

Ionic Bonds

This diagram is another way of showing the electron
transfer that creates an ionic bond:

The dots represents the valence electrons in each atom.

The arrow shows the valence electron of sodium being
captured to become an additional valence electron of
chlorine.

Compounds composed of cations and anions are called ionic
compounds.

Although they are composed of ions with electric charge; ionic
compounds are electrically neutral.

The electrostatic forces that hold ions together in ionic

compounds
are called ionic bonds.

Ionic Bonding

Ionic Compounds

Ionic compounds form crystalline solids at room temperature as
the cations and anions become arranged to maximize the distance
between like charges (which repel) and minimize the distance
between unlike charges (which attract).

Some examples are shown below.

Crystalline ionic solids are very strong and have high melting points
due to the powerful electrostatic forces holding them together.

They are brittle (not easy to bend or shape) since changing their
shape brings the oppositely charged ions closer together.

When oppositely charged ions are forced to be too close together,
the solid shatters.

Hence, while very strong, ionic solids will shatter rather than bend.

Ionic Compounds

At sufficiently high temperature, ionic solids will melt.

Once molten, they have very high boiling points due to the same
electrostatic attractions that made the solid difficult to melt.

Molten Ionic Compounds

Ionic solids can dissolve in water (e.g. salt dissolving in water).

When dissolved, the ions are no long locked into fixed positions, as
they were in the solid crystal.

They are free to move throughout the liquid.

As a result, aqueous solutions of ions can conduct electricity
through the physical movement of those charged ions.

(Ionic solids do not conduct electricity since the ions are not free to
move.)

Aqueous Ionic Compounds

Multiple Choice

Which pair of atoms will form an ionic bond?

• Li and Be

• Na and Mg

• K and Ca

• Na and Cl

Multiple Choice

Which pair of atoms will form an ionic bond?

• Li and Ne

• K and Br

• K and Cs

• S and Cl

Multiple Choice

An ionic bond would form between Sc and F.

• True

• False

• Not enough information

Multiple Choice

Which of the following compounds would you
expect to be ionic?

• H2O

• CO2

• SrCl2

• SO2

Multiple Choice

Which of the following compounds would you
expect to be ionic?

• CO

• NaF

• CH4

• NH3

Multiple Choice

Which of the following compounds would you
expect to be ionic?

• CO

• NO

• LiCl

• SiO2

Multiple Choice

The following are true of ionic solids except:

• They are brittle

• They are strong

• They conduct electricity

• They have a high melting point

Multiple Choice

The following are true of molten ionic compounds
except:

• They are composed of ions

• They are brittle

• They conduct electricity

• They have a high boiling point

Multiple Choice

The following are true of aqueous (dissolved) ionic
compounds except:

• The cations and anions are free to move

• The ions move to conduct electricity

• The solution can conduct electricity

• The anions and cations are locked in position