Covalent Networks

Question 1

Covalent Network Lattices

Answer 1

Common examples of covalent network lattices include diamond, silicon carbide, silicon dioxide (quartz) and tungsten carbide

Diamond: Hardest substance due to bonding pattern of carbon atoms, the structure is rigid in which each carbon atom bonds with four single covalent bonds.

Question 2

Properties of Covalent Network lattices

Answer 2

• Exis as solid with very high melting points and boiling points due to rigid covalent network lattices
• Poor electrical conductivity as there are no free ions or electrons
• Covalent network lattices are hard and brittle as covalent bonds break when lattice is distorted. must be cut in a specific way to not shatter
• Covalent network lattices are chemically inert (stable/not reactive) and are insoluble in water and most other solvents.
• Covalent network lattices such as diamond are good conductors of heat. A collision at one end of a diamond will be effectively transferred through the structure because the atoms are so rigid — bonds do not absorb up the energy of the collision.

Question 3

Covalent layer lattices

Answer 3

• Consist of many atoms held strongly in planes by covalent bonds. Therefore covalent bonding is present in two dimensions. Layers are held together by weaker dispersion forces.

For Example:
* Graphite is an oily black opaque solid made up on only carbon atoms. Each carbon atom is graphite forms three covalent bonds with three other carbons in the same plane. This forms layers of hexagonal rings with strong covalent bonds to form flat sheets in two dimensions. Layers are stacked on top of each other in the crystal lattice, held together by weak dispersion forces.

Question 4

Properties and uses of graphite

Answer 4

• Good conductor of heat and electricity as there are free moving delocalised electrons to carry charge or ransmit energy
• Graphie is soft and slippery as it is held together by strong covalent bonds but weak intermolecular forces. This is why graphite is used as lead in pencils which breaks and transfers onto paper.
• Graphite is inert due to its stable hexagonal rings and delocalised electrons
• High melting point due to srong covalent bonds

Question 5

Allotrope

Answer 5

The different forms that arise from different ways atoms may be bonded together.
* Graphite: Used in lead pencils as well as applications due to electrical conductivity
* Diamond: Covalent network lattice, used for cutting, sawing, or drilling due to hardness.
* Amorphous carbon: Used as charcoal fuel or printing ink.

Question 6

Why are diamonds used to cut/drill into rock?

Answer 6

Extremely hard/durable substance due to extensive covalent bonding in the lattice. Strong covalent bonds will resist a change in structure when force is applied, therefore diamond does nto shatter when used to drill into rock.

Question 7

Why does graphite conduct electricity?

Answer 7

In graphite each Carbon atom forms three covalent bonds, this means that one electron per carbon atom is delocalised. The delocalised electrons can therefore carry the charge throughout the structure, meaning graphite can conduct electricity.

Question 8

Importance of understanding molecular shape

Answer 8

Molecular shape is important in determining how the molecule interacts and reacts with other molecules. Molecular shape also influences the boiling point and melting point of molecules. If all molecules were linear then life as we know it would not exist.