4.3 Covalent Structures

Which of the following substances has a network of covalently bonded atoms?

A. H2O

B. CO2

C. Diamond

D. Methane (CH4)

Which substance is expected to have the lowest melting point due to weak intermolecular forces?

A. Silicon dioxide (SiO2)

B. Diamond

C. CO2

D. Graphite

Which of the following is NOT a property of substances with a network of covalently bonded atoms?

A. High electrical conductivity

B. High melting point

C. High boiling point

D. Hardness

Which of the following substances is a molecular solid with weak intermolecular forces?

A. Graphite

B. Silicon dioxide (SiO2)

C. H2O

D. Diamond

Which substance has layers of covalently bonded atoms that can slide over each other?

A. Diamond

B. CO2

C. Graphite

D. H2O

a) Describe the properties of molecules that exhibit weak intermolecular forces. [2]

b) Explain why substances with weak intermolecular forces, such as H2O and CO2, have low melting and boiling points. [3]

a) What is meant by a "network of covalently bonded atoms"? [2]

b) Using diamond as an example, explain how its covalent structure contributes to its high melting and boiling points. [3]

a) Silicon dioxide (SiO2) is another example of a substance with a network covalent structure. Describe the arrangement of atoms in silicon dioxide. [2]

b) How does the structure of silicon dioxide compare to that of graphite in terms of their melting and boiling points? [3]

a) Why are substances like diamond and graphite, which are both forms of carbon, considered to have network covalent structures? [2]

b) Compare the electrical conductivity of diamond and graphite. Provide a reason for the observed difference. [3]

c) Which of the two, diamond or graphite, is harder and why? [2]

a) Explain the term "intermolecular forces". [2]

b) How do intermolecular forces affect the physical properties of a substance, such as its boiling point? [3]

c) Why does H2O have a higher boiling point than CO2, even though both have weak intermolecular forces? [3]