Main 1LO: Define what ionic solids & molecular solids are

• Work in pairs to study the information on ionic and molecular solids • Jot down key ideas on the worksheet• Answer review questions on your own.

As you know, solids are made of particles packed closely together, in a regular pattern.

Ionic and molecular solidsLO: Define what ionic solids & molecular solids are

The two types of solids have quite different properties.

If the particles are ions, the solids are called ionic solids.

If they are molecules, the solids are called molecular or covalent solids.

LO: Define what ionic solids & molecular solids are

Sodium chloride is made of sodium and chloride ions, packed in a regular pattern repeated millions of times. This arrangement is called a lattice. The ions are held together by strong ionic bonds.

Ionic solids - Structure

A grain of salt zoomed in 500, 000 times

A chloride ion

Strong electrostatic attraction

Cl- Na+

Cl- Na+

Cl- Na+

Cl- Na+

Cl-

Cl-

Na+

Na+

One of the most common ionic solids is sodium chloride-it isordinary table salt.

LO: Define what ionic solids & molecular solids are

1Ionic solids have these properties:

Ionic solids – Their 3 Main properties

They have high melting and boiling points. For example sodium chloride melts at 808°C and boils at 1465°C, sodium hydroxide melts at 319°C and boils at 1390°C.

The reason is that the ionic bonds are very strong, so it takes a lot of heat energy to break up the lattice and form a liquid. That explains why all ionic substances are solid at room temperature.

LO: Define what ionic solids & molecular solids are

2Ionic solids have these properties:

Ionic solids – Their 3 Main properties

They are insoluble in many other solvents, for example in petrol.

They are usually soluble in water.

Ionic solids – Their 3 Main properties

LO: Define what ionic solids & molecular solids are

3Ionic solids have these properties:

They do not conduct electricity, when solid. Electricity is a stream of moving charges. Although the ions are charged, they cannot move, because the ionic bonds hold them firmly in position.

They do conduct electricity when they are melted, or dissolved.This is because the ions are then free to move.

Sugar is a good example of a molecular solid.

Molecular solids - StructureLO: Define what ionic solids & molecular solids are

A close up of an individual molecule of sucrose, C12H22O11 Credit: http://bit.ly/1hFJv9Z

held together by strong covalent bonds.

Each sugar molecule contains • 12 atoms of carbon, • 22 atoms of hydrogen• and 6 atoms of oxygen,

Carbon atom

Oxygen atom

Hydrogen atom

Covalent bond

LO: Define what ionic solids & molecular solids are

Sugar is typical of molecular solids. In all molecular solids, themolecules are held together in a regular pattern repeated millions of times; so the solids are crystalline. The forces that hold the molecules together are weak.

Molecular solids - Structure

A grain of sugar zoomed in 500, 000 times

A sugar molecule

Weak forces of attraction

(Intermolecular forces – attractive force between molecules)

LO: Define what ionic solids & molecular solids are

Molecular solids have these properties:

Molecular solids – Their 3 main properties

1• They have low melting points and boiling points-

much lower than ionic solids do. • In fact many molecular substances melt, and even

boil, below room temperature, so are liquids or gases at room temperature.

• Here are some examples:

Substance Melting point/ C ̊� Boiling point / C ̊�Oxygen -219 -183Chlorine -101 -35Water 0 100Naphthalene 80 218

The reason for these low values is that the molecules are held together by only weak forces, so not much heat energy is needed to separate them.

LO: Define what ionic solids & molecular solids are

Molecular solids have these properties:

2• They do not conduct electricity.

Molecular solids – Their 3 main properties

• Molecules are not charged, so molecular substances cannot conduct, even when melted.

LO: Define what ionic solids & molecular solids are

Molecular solids have these properties:

3• Soft or brittle in solid form

• Because the molecules are held together by only weak intermolecular forces.

Molecular solids – Their 3 main properties

LO: Define what ionic solids & molecular solids are

Molecular substances - Examples• Molecular substance

can also be…

Methane molecules

• Gases

• All of them have weak forces between molecules.

• Liquids