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Giant covalent structures

Dr. Davinder Bhachu & MyEdSpace Chemistry

Teacher

Dr. Davinder Bhachu MyEdSpace Chemistry

Contents

Giant Covalent Molecules (Macromolecules)

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Check Your Understanding

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Giant Covalent Molecules (Macromolecules)

Giant covalent structures are huge 3-D networks in which all atoms are joined by strong covalent bonds. Instead of existing as small, separate molecules, the atoms are linked in a continuous structure (a lattice) that can contain thousands or even millions of atoms.

These substances are sometimes called macromolecules.

Giant Covalent Structures

Key idea:

Simple molecules = small groups of atoms with weak forces between molecules.

Giant covalent structures = every atom covalently bonded (strongly) throughout, making one enormous structure.

No answer provided.

Melting and Boiling Points

Giant covalent structures have very high melting and boiling points because:

  • Every atom is held in place by strong covalent bonds

  • These bonds must be overcome throughout the entire structure to melt or boil the substance

  • This needs a huge amount of energy

Therefore, giant covalent structures are solid at room temperature.

Melting and Boiling Points

Electrical Conductivity

Most giant covalent structures do not conduct electricity because:

  • They have no free electrons

  • They have no ions to carry charge

Exception: some carbon allotropes (graphite) can conduct electricity — but this will be covered in your next note.

Solubility

Giant covalent substances are insoluble in water and other solvents. The covalent bonds are too strong to be pulled apart by water molecules.

Examples

Three common giant covalent structures you need to know are:

Substance

Elements in structure

Notes

Silicon dioxide (SiO₂)

Silicon + oxygen

Found in sand, glass, quartz

Silicon (Si)

Silicon only

Used in computer chips and solar cells

Carbon allotropes (diamond, graphite, graphene)

Carbon only

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Comparison Recap:

Type of substance

Bonding

Forces between particles

MP/BP

Conducts?

Simple molecular

Strong covalent inside molecules; weak forces between molecules

Weak intermolecular

Low

No

Giant covalent

Strong covalent bonds throughout structure

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Very high

No

Exam tip:

When explaining high melting points for giant covalent structures, do not talk about breaking intermolecular forces — mention strong covalent bonds throughout the lattice.

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Check Your Understanding

Q1. What is a giant covalent structure?

A substance where atoms are joined by strong covalent bonds in a continuous 3-D network.

Q2. Explain why giant covalent substances have such high melting points.

Because many strong covalent bonds must be broken throughout the whole structure, which needs a lot of energy.

Q3. Do giant covalent substances conduct electricity? Give a reason.

No — there are no free electrons or ions to carry charge.

Q4. Why are giant covalent substances insoluble in water?

The covalent bonds are too strong to break, so water cannot separate the atoms.

Q5. Which would have the higher melting point: silicon dioxide or oxygen (O₂)? Explain your answer.

SiO₂, because it is a giant covalent structure, not simple molecular — many strong covalent bonds require lots of energy to be broken.

Q6. Put these in order of melting point (lowest → highest): O₂, SiO₂, poly(ethene)

O₂ (lowest) → poly(ethene) → SiO₂ (highest)

Properties of simple molecules (including polymers) Allotropes of carbon