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Muscle fibers, DNA and plastics are all examples of polymers. Watch this video to learn more. A polymer is a large molecule, or macromolecule, composed of many repeated subunits. Because of their broad range of properties, both synthetic and natural polymers play an essential and ubiquitous role in everyday life.

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Giant covalent structures contain a lot of non-metal atoms, each joined to adjacent atoms by covalent bonds covalent bonds: A covalent bond between atoms forms when atoms share electrons to achieve a full outer shell of electrons.. The atoms are usually arranged into giant regular lattices lattice: A lattice is a regular grid-like arrangement of atoms in a material. - extremely strong structures because of the many bonds involved. The graphic shows the molecular structure of diamond and graphite: two allotropes allotropes: Allotropes are structurally different forms of an element. They differ in the way the atoms bond with each other and arrange themselves into a structure. Because of their different structures, allotropes have different physical and chemical properties. of carbon, and of silica (silicon dioxide).

Properties of giant covalent structures

Very high melting points - Substances with giant covalent structures have very high melting points, because a lot of strong covalent bonds must be broken. Graphite, for example, has a melting point of more than 3,600ºC.

[ Variable conductivity - Diamond does not conduct conduct: To allow electricity, heat or other energy forms to pass through. electricity. Graphite contains free electrons electrons: Sub-atomic particles, with a negative charge and a negligible mass relative to protons and neutrons. ] , so it does conduct electricity. Silicon is semi-conductive - that is, midway between non-conductive and conductive.

Graphite

Graphite is a form of carbon in which the carbon atoms form layers. These layers can slide over each other, so graphite is much softer than diamond. It is used in pencils, and as a lubricant lubricant: A substance used to reduce the friction between two solid surfaces.. Each carbon atom in a layer is joined to only three other carbon atoms. Graphite conducts electricity.

Diamond

Diamond is a form of carbon in which each carbon atom is joined to four other carbon atoms, forming a giant covalent structure. As a result, diamond is very hard and has a high melting point. It does not conduct electricity.

Silica

Silica, which is found in sand, has a similar structure to diamond. It is also hard and has a high melting point, but contains silicon and oxygen atoms, instead of carbon atoms.

The fact that it is a semi-conductor makes it immensely useful in the electronics industry: most transistors are made of silica.

Buckminsterfullerene

Buckminsterfullerene is yet another allotrope of carbon. It is actually not a giant covalent structure, but a giant molecule in which the carbon atoms form pentagons and hexagons - in a similar way to a leather football. It is used in lubricants.

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Covalent bonding - giant covalent structures

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Giant covalent structures contain a lot of non-metal atoms, each joined to adjacent atoms by covalent bonds covalent bonds: A covalent bond between atoms forms when atoms share electrons to achieve a full outer shell of electrons.. The atoms are usually arranged into giant regular lattices lattice: A lattice is a regular grid-like arrangement of atoms in a material.

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Covalent bonds [ covalent bonds: A covalent bond between atoms forms when atoms share electrons to achieve a full outer shell of electrons. form between non-metal atoms. Each bond consists of a shared pair of electrons electrons: Sub-atomic particles, with a negative charge and a negligible mass relative to protons and neutrons. ] , and is very strong. Covalently bonded substances fall into two main types:

1. simple molecules molecules: a collection of two or more atoms held together by chemical bonds. The fundamental unit of compounds and

2. giant covalent structures.

Simple molecules

These contain only a few atoms held together by strong covalent bonds. An example is carbon dioxide (CO [ ₂), the molecules of which contain one atom atom: All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. ] of carbon bonded with two atoms of oxygen.

Properties of simple molecular substances

Low melting and boiling points - This is because the weak intermolecular forces break down easily.

Non-conductive - Substances with a simple molecular structure do not conduct conduct: To allow electricity, heat or other energy forms to pass through. electricity. This is because they do not have any free electrons or an overall electric charge.

Higher Tier only

Hydrogen, ammonia, methane and water are also simple molecules with covalent bonds. All have very strong bonds between the atoms, but much weaker forces holding the molecules together. When one of these substances melts or boils, it is these weak 'intermolecular forces' that break, not the strong covalent bonds. Simple molecular substances are gases, liquids or solids with low melting and boiling points.

The animation shows how the weak intermolecular forces between water molecules break down during boiling or melting:

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Covalent bonds [ covalent bonds: A covalent bond between atoms forms when atoms share electrons to achieve a full outer shell of electrons. form between non-metal atoms. Each bond consists of a shared pair of electrons electrons: Sub-atomic particles, with a negative charge and a negligible mass relative to protons and neutrons.

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A secondary school revision resource for AQA GCSE Additional Science about atomic structure and different substances and their properties

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Nanotechnology

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Writing On Hair - Richard Hammond's Invisible Worlds - Series 1 Episode 3 Preview - BBC One

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More about this episode: http://www.bbc.co.uk/programmes/b00rt87x Richard Hammond explores the world of micro design by joining nanotechnologists in writing on a single platelet of a strand of Richardss hair using cutting edge technology.

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BBC - GCSE Bitesize: Metallic bonding - higher

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A secondary school revision resource for AQA GCSE Additional Science about atomic structure and different substances and their properties

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GCSE Science Revision - Solids Liquids and Gases

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BBC Bitesize - GCSE Chemistry (Single Science) - Covalent bonding and the periodic table

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An introduction to covalent bonding, focussed on the periodic table.

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Through animations of atoms of sodium and chlorine we see how an ionic bond is formed. We then see how gaining and losing electrons leads to positively and negatively charged ions. Only the formation of singularly charged ions is mentioned.We also find out that only metals and non-metals can form ionic compounds.

This clip could be used to introduce the concept of ionic bonding. After watching it, students could be asked to draw atomic diagrams to show the formation of ions.

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BBC Bitesize - GCSE Chemistry (Single Science) - Ionic compounds and the periodic table

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Through animations of atoms of sodium and chlorine we see how an ionic bond is formed. We then see how gaining and losing electrons leads to positively and negatively charged ions. Only the formation of singularly charged ions is mentioned.We also find out that only metals and non-metals can form ionic compounds.