Module 2 - Ionic Bonding and Structure

Question 1

Define an ionic bond.

Answer 1

Ionic bonding is the strong electrostatic attraction between oppositely charged ions (cations and anions).

Question 2

State common cations:

Answer 2

• metal ions (Na^2+, Ca^2+, Al^3+)

- ammonium ions (NH4^+)

Question 3

State common anions:

Answer 3

• non-metal ions (Cl^-, O^2-)

- polyatomic ions (NO3^-, SO4^2-)

Question 4

Describe ionic compound formation.

Answer 4

-The simplest ionic compounds contain metal ions and non-metal ions, and involve electron transfer.
=Outer shell electrons from a metal atom are transferred to the outer shell of a non-metal atom.
=Positive and negative ions are formed.
=The ions formed often have outer shells with the same electron configuration as the nearest noble gas.

Question 5

Structure of ionic compounds:

Answer 5

• Each ion in an ionic compound attracts the oppositely charged ions in all directions.
• The result is a giant ionic lattice.

Question 6

Example: Describe the structure of NaCl

Answer 6

NaCl:

• Each ion is surrounded by oppositely charged ions, forming a giant ionic lattice.
• Each Na^+ ion is surrounded by 6 Cl^- ions.
• Each Cl^- ion is surrounded by 6 Na^+ ions.

Question 7

Properties: Melting and boiling points:

Answer 7

• Almost all ionic compounds are solids at room temperature and have high melting and boiling points.
• This is because ionic compounds have strong electrostatic forces of attraction between the oppositely charged ions in the giant ionic lattice.
• High temperatures are therefore needed to provide the large quantity of energy needed to overcome the strong electrostatic attraction between the ions.

Question 8

Example of melting points:

Answer 8

NaF ; Na^+ F^- ; m.p. = 993
CaF2 ; Ca^2+ F^- ; m.p. = 1423
Na20 ; Na^+ O^2- ; m.p. = 1275
CaO ; Ca^2+ O^2- ; m.p. = 2614

Question 9

What is the pattern for ionic compounds and their melting points?

Answer 9

• The melting points are higher for lattices containing ions with greater ionic charges, as there is a stronger attraction between the ions.
• Ionic attraction also depends on the size of the ions.

Question 10

What does solubility require?

Answer 10

Solubility requires 2 main processes:

• the ionic lattice must be broken down.
• water molecules must attract and surround the ions.

Question 11

Polar solvents:

Answer 11

• Many ionic compounds dissolve in polar solvents, such as water.
• Polar water molecules break down the lattice and surround each ion in solution.
• In a compound made of ions with large charges, the ionic attraction may be too strong for water to be able to break down the lattice structure.
• Thus the compound will not be very soluble.

Question 12

What does solubility depend on?

Answer 12

• The solubility of an ionic compound in water therefore depends on the relative strengths of the attractions within the giant ionic lattice and the attractions between ions and water molecules.
• Generally, as the attractions in the giant ionic lattice have greater effect, (ionic charges increasing), solubility decreases. But this is not always the case.

Question 13

Electrical Conductivity:

Answer 13

• In the solid state, an ionic compound does not conduct electricity.
• When molten or in solution, ionic compounds do conduct.

Question 14

In the solid state…

Answer 14

• the ions are in a fixed position in the giant ionic lattice.
• there are no mobile charge carriers.

Question 15

In the liquid state or dissolved in water…

Answer 15

• the solid ionic lattice breaks down.

- the ions are now free to move as mobile charge carriers.

Question 16

Summary of properties:

Answer 16

Most ionic compounds:
=have high m.p. and b.p.
=tend to dissolve in polar solvents such as water.
=conduct electricity only in the liquid state or in aqueous solution.