PHYSICAL PROPERTIES RELATED TO STRUCTURE AND BONDING

Question 1

Metallic lattices are…

Answer 1

composed of a regular arrangement of positive metal ions surrounded by delocalised electrons.

Question 2

Substances that have a giant metallic lattice have what properties?

Answer 2

• High melting/boiling temperature.
• Good electrical conductivity.
• Good thermal conductivity.
• Malleability.
• Ductility.

Question 3

Giant ionic lattices are…

Answer 3

composed of a regular arrangement of positive and negative ions.

Question 4

Substances that have a giant ionic lattice have what properties?

Answer 4

• Fairly high melting temperatures
• Brittleness
• Poor electrical conductivity when solid but good molten.
• Often soluble in water.

Question 5

What are giant covalent lattices?

Answer 5

They consist of a giant network of atoms linked to each other by covalent bonds.

Question 6

Four of the most common giant covalent substances are..

Answer 6

• Diamond
• Graphite
• Graphene
• Silicon oxide

Question 7

What is the structure of diamond and bond angles?

Answer 7

In diamond each carbon atom forms four sigma bonds to four other carbon atoms, in a giant three-dimensional tetrahedral arrangement. All bond angles are 109.5 degrees.

Question 8

Why does diamond have a high melting point and is very hard?

Answer 8

Diamond is extremely hard because of the very strong C-C bonding throughout the structure. It has a high melting temperature because a great number of strong C-C bonds have to be broken in order to melt it. This requires a large amount of heat energy.

Question 9

What structure does graphite have?

Answer 9

layered structure.

Question 10

Explain the structure of graphite?

Answer 10

-Each carbon atom is bonded to 3 others by sigma bonds, forming interlocking hexagonal rings. The fourth electron on each carbon atom is in a p-orbital. The carbon atoms are close enough to overlap with one another to produce a cloud of delocalised electrons above & below the plane of the rings.

Question 11

Why can graphite be used as a solid lubricant?

Answer 11

The layers slide easily over one another.

Question 12

Why does graphite’s ability to act as a lubricant decrease at altitude or in a vacuum?

Answer 12

Because it’s lubricating abilities are as a result of absorbed gases on the surface of the carbon atoms.

Question 13

Why is graphite a fairly good conductor of electricity?

Answer 13

Because the delocalised electrons between the layers are free to move under the influence of an applied potential difference.

Question 14

Why can graphite only conduct electricity parallel to its layers?

Answer 14

Because unlike a metal the delocalised electrons are not free to move from one layer to the next.

Question 15

What is graphene?

Answer 15

Pure carbon in the form of a very thin sheet one atom thick.

Question 16

What is the structure of iodine?

Answer 16

Iodine exists as diatomic molecules, in solid iodine these molecules are arranged in a regular pattern.
-The structure is described as ‘face-centred cubic’. In practice the iodine molecules will be touching one another. The molecules of iodine are held together by London forces.

Question 17

What are the physical properties of molecular solids?

Answer 17

• Generally have low melting/boiling temps.
• In order to melt a molecular solid it is not necessary to break the covalent bonds within the molecules, it is only necessary to overcome the intermolecular forces of attraction.
• Little energy is required to break the force of attraction to separate the molecules and cause a liquid to boil and vaporise.

Question 18

Why do macromolecules have higher melting temperatures than a monomer?

Answer 18

London forces increase with both an increase in the number of electrons.