AQA · Chemistry · 8462
GCSE Chemistry (AQA): Types of Covalent Structures
Topic 2 — Bonding, Structure & Properties of Matter. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Types of Covalent Structures: Simple Molecular & Giant Covalent Structures"; each card deep-links to the moment in the video it came from. Lesson 2.07 of Cognito's AQA GCSE Combined Science (Trilogy) and Chemistry course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-c_2.07.
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In what ratio are silicon and oxygen atoms present in silicon dioxide?
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One silicon to two oxygen (SiO₂). It is also called silica and is the main component of sand.
Which giant covalent structure is the exception that conducts electricity?
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Graphite.
Why do simple molecular substances have low melting and boiling points?
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Only the weak intermolecular forces between molecules must be overcome, which needs little energy.
How are the atoms arranged in a giant covalent structure?
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Huge numbers of non-metal atoms all covalently bonded to each other in a regular repeating lattice.
Why do giant covalent structures have very high melting and boiling points?
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Melting them requires breaking many strong covalent bonds throughout the lattice, which takes a great deal of energy.
The weak forces of attraction between separate molecules are called ? forces.
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intermolecular
Why do boiling points increase down Group 7 (the halogens)?
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The molecules get larger, so there are more intermolecular forces to break, requiring more energy.
What must a substance contain in order to conduct electricity?
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Charged particles — electrons or ions — that are free to move.
Why do simple molecular substances not conduct electricity?
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They have no free electrons and the molecules carry no overall electric charge, so there are no charged particles free to move.
What is a simple molecular substance?
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A substance made of small molecules containing just a few covalently bonded atoms, e.g. chlorine or ammonia.
Name three examples of giant covalent structures.
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Diamond, graphite and silicon dioxide.
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