Properties of small molecules (5.2.2.4) | AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Higher | KnowledgeSet

Properties of small molecules

Chemistry (Combined Science) · GCSE · AQA · AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Higher · Specification point · 5.2.2.4 · Bonding, structure, and the properties of matter · How bonding and structure are related to the properties of substances

Melting and boiling in small molecular substances

Electrical conductivity of small molecular substances

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Learning Objectives

5.2.2.4 Properties of small molecules

Content	Key opportunities for skills development
$Substances that consist of small molecules are usually gases or liquids that have relatively low melting points and boiling points. These substances have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils. The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points. These substances do not conduct electricity because the molecules do not have an overall electric charge. Students should be able to use the idea that intermolecular forces are weak compared with covalent bonds to explain the bulk properties of molecular substances.$	$WS 1.2$

Content

Key opportunities for skills development

Substances that consist of small molecules are usually gases or liquids that have relatively low melting points and boiling points. These substances have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils. The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points. These substances do not conduct electricity because the molecules do not have an overall electric charge. Students should be able to use the idea that intermolecular forces are weak compared with covalent bonds to explain the bulk properties of molecular substances.

WS 1.2