Structure and Properties

Solid Lattices

What are the four main types of bonding and structure in solids?

Giant metallic, giant ionic, giant covalent and molecular.

What particles are present in a giant metallic structure?

Positive metal ions and delocalised electrons.

What particles are present in a giant ionic structure?

Positive and negative ions.

What particles are present in a giant covalent structure?

Atoms.

What particles are present in a molecular structure?

Discrete molecules.

What type of bonding is present in a giant metallic structure?

Metallic bonding.

What type of bonding is present in a giant ionic structure?

Ionic bonding.

What type of bonding is present in a giant covalent structure?

Covalent bonding.

What type of bonding is present within molecules in a molecular substance?

Covalent bonding.

What forces exist between molecules in a molecular substance?

Intermolecular forces.

What are the typical melting and boiling temperatures of giant metallic substances?

Fairly high to high.

What are the typical melting and boiling temperatures of giant ionic substances?

Fairly high to high.

What are the typical melting and boiling temperatures of giant covalent substances?

High to very high.

What are the typical melting and boiling temperatures of molecular substances?

Generally low.

Why do giant metallic structures have relatively high melting temperatures?

Strong electrostatic attractions between positive metal ions and delocalised electrons require a large amount of energy to overcome.

Why do giant ionic structures have high melting temperatures?

Strong electrostatic attractions between oppositely charged ions require a large amount of energy to overcome.

Why do giant covalent structures have very high melting temperatures?

Many strong covalent bonds throughout the giant lattice must be broken, requiring a large amount of energy.

Why do molecular substances generally have low melting and boiling temperatures?

Only relatively weak intermolecular forces between molecules need to be overcome.

Do giant metallic structures conduct electricity when solid?

Yes, because their delocalised electrons are free to move through the structure and carry charge.

Do giant metallic structures conduct electricity when molten?

Yes, because the delocalised electrons remain mobile and can carry charge.

Do giant ionic structures conduct electricity when solid?

No, because the ions are held in fixed positions and cannot move to carry charge.

Do giant ionic structures conduct electricity when molten?

Yes, because the ions become mobile and can carry electrical charge.

Do giant covalent structures normally conduct electricity?

No, because they generally have no mobile charged particles.

What is an important exception to the electrical conductivity of giant covalent structures?

Graphite and graphene conduct electricity because they contain mobile delocalised electrons.

Do molecular substances normally conduct electricity?

No, because they do not contain mobile charged particles.

Are giant metallic substances soluble in water?

Generally no; however, some metals react with water rather than simply dissolving.

Are giant ionic substances soluble in water?

Generally yes, although there are important exceptions such as AgCl, AgBr, AgI and BaSO₄.

Are giant covalent substances soluble in water?

Generally no.

Are molecular substances soluble in water?

Generally insoluble, although some dissolve if they can form favourable interactions such as hydrogen bonds with water.

Why can sucrose dissolve in water?

Sucrose can form hydrogen bonds with water molecules.

How can electrical conductivity help identify the bonding and structure of a substance?

A substance that conducts when both solid and molten is likely metallic; one that conducts only when molten is likely ionic; one that does not conduct in either state is likely giant covalent or molecular.

If a substance conducts electricity when solid, what type of structure is it most likely to have?

A giant metallic structure.

If a substance does not conduct when solid but conducts when molten, what type of structure is it most likely to have?

A giant ionic structure.

If a substance does not conduct when solid or molten, what two structures are most likely?

Giant covalent or molecular.

How can melting temperature distinguish between giant covalent and molecular substances?

Giant covalent substances usually have very high melting temperatures, whereas molecular substances generally have low melting temperatures.

What information should you use to predict the bonding and structure of an unknown substance?

Melting and boiling temperatures, electrical conductivity when solid and molten, and solubility in water.

Why should several physical properties be considered when identifying bonding and structure?

Individual properties can have exceptions, so using several properties gives a more reliable identification.

A substance has a high melting temperature and conducts electricity both when solid and molten. What structure is most likely?

Giant metallic.

A substance has a high melting temperature, does not conduct when solid but conducts when molten. What structure is most likely?

Giant ionic.

A substance has a very high melting temperature and does not conduct electricity when solid or molten. What structure is most likely?

Giant covalent.

A substance has a low melting temperature and does not conduct electricity. What structure is most likely?

Molecular.

Substance A melts at 1083°C, conducts electricity when solid and molten, and is insoluble in water. What structure is most likely?

Giant metallic.

Substance B melts at 119°C, is a poor conductor when solid and molten, and is insoluble in water. What structure is most likely?

Molecular.

Substance C melts at 2230°C, is a poor conductor when solid and molten, and is insoluble in water. What structure is most likely?

Giant covalent.

Substance D melts at 801°C, is a poor conductor when solid but a good conductor when molten, and is soluble in water. What structure is most likely?

Giant ionic.

Why is Substance A likely to be metallic?

It conducts electricity in both the solid and molten states and has a high melting temperature, characteristic of a giant metallic lattice.

Why is Substance B likely to be molecular?

It has a relatively low melting temperature and does not conduct electricity.

Why is Substance C likely to be giant covalent?

It has a very high melting temperature, does not conduct electricity and is insoluble in water.

Why is Substance D likely to be ionic?

It has a high melting temperature, does not conduct when solid, conducts when molten and is soluble in water.

What is an important exam warning when identifying structure from physical properties?

There can be exceptions, so use all of the information given rather than relying on a single property.

Why might a metal appear to be soluble in water?

It may actually react with water to form a soluble metal hydroxide rather than simply dissolving.

Why can some substances have properties that are unusual for their expected bonding type?

Physical properties depend on the particular structure and particles present, so general bonding rules have exceptions.