Chapter 5 - Covalent Network Substances

Question 0

Properties of covalent network substances:

Answer 0

Very high boiling and melting points.
Non conductors of electricity in solid or liquid state
Extremely hard and brittle
Reasonably chemically inert
Insoluble in water and most other solvents

Question 1

Explain covalent network substances

Answer 1

Silicon dioxide is a covalent network substance. Silicon, having an ale torn configuration 2 8 4 needs to gain 4 electrons to attain 8 electrons in its outer shell. Oxygen with a electron config. of 2 6 needs 2 electrons to attain a full outer shell. As a result each silicon atom forms single covalent bonds with four oxygen atoms and each oxygen atom forms single covalent bonds with two silicon atoms, these atoms are not bonded in small molecules, instead they are bonded in a large network lattice

Question 2

Explain high melting points and hardness of covalent network substances

Answer 2

Each atom is held in the rigid lattice by the strong covalent bonds. To break these bonds requires a very large amount of energy. However, if some of the covalent bonds are broken, then the network lattice is placed under stress and rather than changing shape, the solid shatters.

Question 3

Explain non conductors of heat

Answer 3

In a covalent network substance the electrons are either inner shell electrons or localised in the bonding and non bonding pairs around each atom. As a result, the electrons cannot act as charge carriers in the conduction of electricity. There are also no ions present in the lattice.

Question 4

What is a pure substance

Answer 4

Pure substances consist of matter that is homogenous and has a definite fixed composition. Elements are pure substances. Compounds are pure substances composed of two or more elements chemically combined in fixed proportions.

Question 5

What are mixtures

Answer 5

Matter composed of two or more pure substances is described as a mixture. Mixtures can contain different proportions of the same component substances. Seawater is an example of a mixture, because the amount of salt dissolved in the water may vary.

Question 6

Explain homogenous substances

Answer 6

They have uniform composition and properties throughout and are known as solutions.

Question 7

Explain heterogenous mixtures

Answer 7

They are not uniform in composition nor properties throughout.