Chemistry (C3) - Structures

This set of notes is for C3 Chemistry, GCSE, AQA and specifically, Structures. This topic has six subtopics which are:

Simple Molecular Substances          Ionic Substances          Covalent Structures          Metals and Alloys          Polymers          Nanoscience

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Simple Molecular Substances

Molecules are two or more atoms joined by covalent bonds, which is where two electrons are shared between two atoms joining the two atoms together.

Covalent bonds are very strong and if broken, there is a chemical change as new substances are formed. 

Inbetween these molecules they are joined together with other molecule by weak intermolecular forces which are weaker than the main three types of bonding.

When substances boil or melt it is these intermolecular forces tha break, not the covalent bonds. 

Simpler molecular substance have lower melting point.

Molecules do not conduct electricity.

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Ionic Substances

Ions contain different amounts of electrons and protons so can conduct electricity. 

Ionic substances are made of both metals and non-metals so are compounds.

All ionic compounds are solids at room temperature (ex, house hold salt).

Ionic compounds are packed together in an ordered structure.

Each ion is next to another with opposite attraction so they are attracted to eachother by electrostatic attraction (oppositely charged ions attracted to eachother, ionic bonding).

The force between the oppositely charged ions is strong and to melt and boil the ionic compound, these forces must be overcome which takes lots of energy.

This gives them high melting / boiling points.

Ions are electrically charged particles. An electric current is the flow of electrically charged ions. In the form of a solid, the particles cannot flow, however if the ionic compound was melted or dissolved in a solution the ions are free to move so the ionic compund is an electrical conductor.

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Covalent Structures - Introduction and Fullerenes

Non-metals can covalently bond to form molecules or giant covalent structures.

Giant covalent structures is where all the atoms are covalently bonded in a massive structure.

In order to melt or boil a giant covalent structure, many covalent bonds have to be broken which is very difficult.

Fullerenes are an example of giant covalent structures as the are made of carbon rings. 

Since the original discovery, more have been made.

They are useful as lubricants and catylists.

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Covalent Structures - Diamond and Graphite

Diamond: Structure: Each carbon atom is covalently bonded to four other.

Melting Point: Very high as lots of strong covalent bonds have to be broken.

Hardness: Very hard as the atoms are bonded in a rigid network.

Electrical Conductivity: Insulator, there are no free electrons.

Graphite: Structure: Each carbon atom is covalently bonded to three others, leaving the spare electron with each atom to be free, forming layers which are free to slide over eachother as they are not bonded together but held together with the negative charge of the free electron.

Melting Point: Very High as lots of covalent bonds have to be broken.

Hardness: Soft ad slippry as the layers can slide over eachother.

Electrical Conductivity: Conductor, there is one free electron to move along the layers.

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Metals and Alloys

Metals conduct heat and electricity as the outer shell electron delocolises so therefore can move around. 

Metals are also arranged in layers so can be bent and hammered into shape, however they often bend too well to be useful which is why we make alloys

An alloy is a mixture of a metal with other elements, usually differnt metals or carbon.

The different atoms added are a different size to the metal so will ruin the layered structure, this makes the alloy harder.

There also shape memory alloys where the alloy returns to its original form after being deformed by heating or warming the object.

An  example is nitonol, used for teeth as they move the the shape the teeth should be. 

Nitonol is faster at correcting the teeth and the braces are more comfortable.

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Polymers have a wide range of uses like plastic bags, bottles, but their properties are defined by their structure.

Their structure depends on their original monomer (alkene).

Their structure also depends on the conditions (temperature / pressure) when being made.

If the temperature and pressure are higher then the polymer will be softer. 

There are two main types of polymers, thermosoftening and thermosetting. 

Thermosoftening polymers are where the long strands of polymers do not join with eacother, meaning they are soft  with low melting points so can be recycled.

Thermosetting polymers are where the longs strands do join by strong covalent bonds called cross-links. They have high melting point so cannot be recycled.

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Nanoscience - Introduction

Nanoscience is the study of nanoparticles which are 1-100 nm in size. They are too small to be seen.

Nanoparticles do not share the same properties. They have:

different colours          different strengths          different reactions          different elcrical / thermal conductivity.

There are many concerns with nanoscience. Since each nanoparticles have different properties in bulk it is possible some may be toxic.

Since they are very small, the toxic nanoparticles may slip through the skin and cell membranes.

For this to be made sure, further research is needed.

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Nanoscience - Uses

Nanoparticles are used for:

Sun block: Titanium dioxide blocks out UV rays from the sun, these types of sunblock are colourless. 

Bacteria Killing: Silver nanoparticles are put into clothes to kill bacteria and prevet smells. Silve nanoparticles are also being developed in deodorants.

Coatings: Some windows are layered with titanium dioxide which washes off dirt using rainfall. 

Catylists: Gold nanoparticles speeds up reactions without getting used up. 

Sensors: Gold nanoparticles detect toxic lead ions however the sensors are specific on what they detect.

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