Covalent Network Substances

Flashcards about covalent network substances, their properties, and allotropes of carbon.

What are covalent network substances?

Substances made of atoms covalently bonded in a continuous three-dimensional lattice, not consisting of discrete molecules.

Give examples of covalent network substances.

Diamond, graphite, silicon dioxide (SiO₂), and silicon carbide (SiC).

What are the general properties of covalent network substances?

Hard and brittle, high melting and boiling points, poor conductors of electricity (except graphite), and insoluble in water.

Why are covalent network substances hard and brittle?

Atoms are held together in a rigid 3D lattice by strong covalent bonds, making them extremely hard. When force is applied, the structure tends to shatter rather than bend due to its inflexibility.

Why do covalent network substances have high melting and boiling points?

The continuous network of strong covalent bonds requires a large amount of energy to be broken, resulting in very high melting and boiling points.

Why are most covalent network substances poor conductors of electricity?

They do not have free-moving electrons or ions; electrons are held tightly in covalent bonds and cannot move to conduct electricity (exception: graphite).

Why are covalent network substances insoluble in water?

The strong covalent bonds in the lattice are not broken by interactions with water molecules, making them insoluble.

What are allotropes?

Different structural forms of the same element in the same physical state, occurring when atoms of the element are bonded together in different ways.

Give examples of carbon allotropes.

Diamond, graphite, graphene, fullerenes, and carbon nanotubes (CNTs).

Explain a property of diamond.

Very hard (the hardest natural substance), has a very high melting and boiling point, and cannot conduct electricity.

Explain why diamond is hard and has a high melting point.

All electrons in the outer shell of each carbon atom are involved in forming strong covalent bonds, requiring a lot of energy to break.

Explain a property of graphite.

Soft and slippery, conducts electricity (the only non-metal to do so).

Explain why graphite is soft and conducts electricity.

Only three of the four electrons in the outer shell of each carbon atom are involved in covalent bonds, leaving free electrons for conductivity, and weak forces between layers allow them to slide easily.

Describe the structure of diamond.

Each carbon atom is bonded to 4 others in a tetrahedral arrangement, forming a strong 3D network.

Describe the structure of graphite.

Each carbon atom is bonded to 3 others in a layered hexagonal arrangement, with strong covalent bonds within layers and weak forces between layers.

How does the bonding in diamond and graphite relate to their different uses?

Diamond's strong 3D network makes it suitable for cutting tools and jewellery, while graphite's layered structure and conductivity make it useful as lubricants, in pencils, and as electrodes.

Give other examples of covalent network substances besides carbon allotropes.

Silicon Dioxide (SiO₂) and Silicon Carbide (SiC).

What is silicon dioxide (SiO₂)?

Forms a strong 3D network of Si and O atoms; very hard and high melting point; found in sand (quartz).

What is silicon carbide (SiC)?

Similar strong lattice with alternating Si and C atoms; used in abrasives and cutting tools.

What are fullerenes?

Molecules made entirely of carbon in the form of hollow spheres or tubes (e.g. C₆₀, also known as buckyballs).

What are carbon nanotubes (CNTs)?

Cylindrical nanostructures made by rolling graphene sheets; extremely strong, lightweight, and excellent electrical and thermal conductors.

What is graphene?

A single layer of carbon atoms arranged in a two-dimensional honeycomb lattice; incredibly strong, nearly transparent, and conducts electricity and heat better than any other material.

Describe the properties of Covalent Molecular substances.

Strong bonding within molecules, weak bonding between them, resulting in a low melting point, poor electrical conductivity, and variable solubility in water.

Describe the properties of Covalent Network substances.

Strong covalent bonds in a 3D lattice, resulting in very high melting point, poor electrical conductivity (except graphite), and insolubility in water.

Which type of covalent substance would be better suited for high-heat applications and why?

Covalent network substances, because they have very high melting points due to the strong covalent bonds in their 3D lattice.