Structure Decides
How the structure and bonding of a substance explain its properties: why giant ionic and giant covalent structures melt at high temperatures, why simple molecules melt low, and why metals and molten ionic compounds conduct electricity.
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Structure decides properties
Why does salt melt at a high temperature but wax melts in your hand? Why does copper conduct electricity but sugar does not? The answer is always the structure and the bonding inside the substance. This module works through the main structures and shows how each one explains the properties you can measure.
Structure vocabulary
Learn these four structures before you study their properties.
High melting or low
The structure decides how much energy is needed to melt a substance.
Always link the chain
A top answer never states a property on its own. It runs the chain: structure, then bonding, then property. Ionic compounds conduct only when molten or dissolved because only then are the ions free to move. A high melting point comes from many strong bonds that need a lot of energy to break. Name the structure, name the bonding, then explain.
Match the property
- giant ionic
- simple molecular
- giant covalent
- metallic
- high melting point, conducts only when molten or dissolved
- low melting point and does not conduct
- very high melting point from many strong bonds
- conducts electricity and can be bent into shape
Match the example
- sodium chloride
- oxygen gas
- diamond
- copper
- a giant ionic lattice
- a simple molecule
- a giant covalent network
- a metallic structure
When does ionic conduct?
Why does an ionic compound conduct electricity only when it is molten or dissolved?
- The ions become free to move and carry charge.
- The ions move freely in the solid too.
- It has a sea of delocalised electrons.
- It never conducts under any conditions.
Giant covalent facts
Select the TWO statements that are true of a giant covalent structure.
- It has many strong covalent bonds.
- It has a very high melting point.
- It melts at a very low temperature.
- It is held together by weak forces.
Order the reasoning
Put the steps of a top structure-and-bonding answer in order, earliest first.
- Name the structure of the substance
- Name the bonding that holds it together
- State how strong the forces are
- Explain the property this gives
Complete the facts
A giant _____ lattice has a high melting point and conducts only when molten or dissolved. A simple _____ substance melts low because the forces between molecules are _____. A giant _____ structure melts very high because it has many strong bonds. A metal conducts because it has a sea of delocalised _____.
Liquid range
Sodium chloride, an ionic compound, melts at about 801 degrees and boils at about 1465 degrees. Subtract 801 from 1465 to find the range over which it stays liquid. What is the answer in degrees?
Spot the conductors
Tap the TWO that conduct electricity.
- solid copper
- molten sodium chloride
- solid sodium chloride
- oxygen gas
Name the structure
Read each set of properties and choose the structure that explains them.
- A substance has a high melting point and conducts only when molten or dissolved. What is its structure?
- A substance melts at a low temperature and never conducts electricity. What is its structure?
- A substance conducts electricity and can be bent and shaped without breaking. What is its structure?
Explain a property
Explain why a giant ionic compound has a high melting point and conducts electricity only when molten or dissolved.
- Describe the structure and the bonding
- Explain the high melting point from the strong forces
- Explain why it conducts only when molten or dissolved