2.2.8 Structures of Covalent Bonds

Question 1

Name two types of covalent structure and produce examples of them.

Answer 1

1. A simple molecular lattice - made up of smaller units of Ne, H2, O2, N2 or H2O
2. A giant covalent lattice
   - diamond, graphite and SiO2

Question 2

What are the bonds like in simple molecular substances?

Answer 2

1. Atoms within each molecule are held together via strong covalent bonds
2. The different molecules = held togeth by weak IM Van der Waals’ or London forces
   （eg. In I2) which break when it changes state

Question 3

What are the melting points of simple molecular structures like?

Answer 3

Low, because they have weak IM forces between the molecules, so small amounts of en are needed to break them.

Question 4

What is the electrical conductivity of all covelant molecules like?

Answer 4

They are all non conductors, as there are no delocalised electrons available to move. THE ONLY EXCEPTION IS GRAPHITE.

Question 5

Why does graphite conduct electricity?

Answer 5

Delocalised electrons between the layers are able to move freely (coordination number of 3, so each one has a spare electron to move) and parallel to the layers when = p.d

Question 6

What is the solubility of simple covalent molecules like?

Answer 6

They are only soluble in non-polar solvents such as hexane, because weak London forces form between the covelant molecules and the solvents, so larger covelant structure is broken appt. Both simple m lattices and these solvents have weak Van der Waals’ forces; ‘Like dissolves like’

Question 7

What are the melting points of giant covalent structures like?

Answer 7

High, because high temperatures are needed break strong cov bonds

Question 8

What is the solubility of giant covalent structures like and why?

Answer 8

They are insoluble in polar and non polar, as cov bonds are too strong be broken by either polar or non polar solvents.