AQA Chemistry - Bonding, Structure and Properties of Matter

When metals react with non metals, they form ionic bonds through ionic bonding. 

• Ionic bonding involves the transfer of electrons from the metal to the non metal. 
• The metal loses their outer electrons while the non-metal atoms gain their electrons in order to achieve a full outer shell.
• A giant ionic lattice is formed - which has strong electrostatic forces between the positive ions and the negative ions which keeps the ions in place. 
• It is very difficult to overcome these strong electrostatic forces

Properties of Ionic compounds

• High melting and boiling points:
  A high temperature is required to overcome the strong electrostatic forces between oppositely charged ions

• Do not conduct electricity when solid - only when molten or dissolved in water (aq)
  The ions cannot move freely, because of electrostatic forces - can only vibrate. When molten, the ions are free to move and carry charge throughout the structure. 

The Dot and Cross model:

• Advantages: Shows how ionic bonds are formed, and the ratios that they react with,
• Disadvantages: 2D, Ions are not shown to be spaced out, and not to scale.

Ball and Stick

• Advantages: 3D, Arranged in a lattice formation, and shows different ions clearly
• Disadvantages: No physical sticks between the ions as shown in the diagram, doesn't show movement of electrions, and not to scale. 

Space Filling 

• Advantages: 3D, shows how much space each atom occupies
• Disadvantages: Atoms are not inelastic or spherical or solid as shown in the diagram. 

Metals consists of giant structures of atoms that are arranged into a regular pattern or lattice. 

• In a metal, there are positive metal ions, and negative delocalised electrons from the outer shell, making the metal atoms into positive ions.
• This creates a strong electrostatic bond between the positive ions and the sea of delocalised electrons

Properties of Metal Compounds

• High melting and boiling points
  There are strong electrostatic forces between the positive metal ions and the sea of delocalised electrons that require a large amount of energy to be overcome.
• Pure metal conducts Electricity and Heat
  The sea of delocalised electrons is free to move throughout the lattice and can carry charge. They can also carry thermal energy in the same way. 
• Pure metals are very malleable and ductile
  Layers of metal atoms can slide past each other without disrputing the metallic structure. 

Metals are malleable - the layers of metal atoms can slide past each other without disrupting the metallic structure - because they are in a regular pattern.

• This means that metals are soft and ductile - can be drawn into thin wires. 

Alloys are a mixture of metals

• The different sizes of atoms distort the regular pattern of the metals
• This makes it more difficult for the metal atoms to slide over each other
• This makes alloys harder than pure metals,
• Therefore, metals can be used in a useful manner. 

• A covalent bond is a shared pair of electrons.
• A molecule is a group of two or more non-metal atoms which are held together by strong covalent bonds.
• Weak forces of attraction exist between the molecules and these are known as weak intermolecular forces.
• Covalent compounds do not conduct electricity because they are formed between non-metal atoms by sharing of electrons. Covalent compounds have no free electrons and hence they do not conduct electricity

Simple Molecular Properties

• Low melting and boiling points
  Not a lot of energy is required to overcome the weak intermolecular forces between molecules.
• Do not conduct electricity
  There are no delocalised outer electrions and there are no ions, so charge cannot flow. Molecules have no overall charge - no ions.
• Insoluble in water

2D Ball and Stick

• Advantages: Shows how so many atoms are bonded to so many other atoms
• Disadvantages: Does not show electrons, it is not 3D, suggests atoms are all one size.

3D Ball and Stick

• Advantages: Shows true 3D shapes and bonding angles.
• Disadvantages: Suggests atoms are the same size, no electrons shown. 

Dot and Cross - outer shell electrons

• Advantages: Shows electron sharing
• Disadvantages: The dots and cross imply the electrons are different, they are the same.

Dot and Cross - outer shell electron with shells

• Advantages: Shows atoms are different sizes, shows the idea of energy levels.
• Disadvantages: Implies by the dots and crosses that the electrons are different somehow. 

Diamond is a giant covalent structure - it is a macromolecular structure.

It only contains carbon atoms - only consisting of one element. 

Physical properties of diamond linked to structure and bonding:

• Hard this is because all the carbon atoms are held in place by four, strong covalent bonds in a rigid network
• High melting and boiling points - this is because a lot of energy is required to overcome the strong covalent bonds. 
• Does not conduct electricity - this is because there are no delocalised electrons (the carbon has made four covalent bonds), and therefore, there are no extra electrons that can carry the charge throughout the structure. 

Graphite is a giant covalent structure - it is macromolecular. 

Graphite makes bonds to three carbon, which means that there is one free electron which can be move throughout the structure and carry charge.

Graphite consists of carbon only - single element. 

Physical properties and links to structure and bonding present:

• Soft and slippery - there are weak intermolecular forces between the layers, so they can slide easily.
• High melting and boiling points - there are strong covalent bonds between the atoms that are hard to overcome - they require a lot of energy. 
• Good conductor of electricity - There is one free electron that is not "covalently" bonded, so it is free to move around the structure and carry charge. 

Silicon dioxide is a giant molecular structure - it is macromolecular 

Silicon dioxide is consisted of silicon and oxygen - compound. 

Silicon makes four covalent bonds to oxygen - the ratio one silicon to two oxygens. 

Physical properties and links to structure and bonding present:

• High melting points - Strong covalent bonds which require a lot of energy to overcome. 
• Very hard - Due to strong covalent bonds which require a lot of energy to overcome. 
• Does not conduct electricity - There are no delocalised electrons to carry charge throughout the structure. 

Fullerenes are molecules of carbon atoms with hollow shapes - their structures are based on hexagonal rings of carbon atoms joined by covalent bonds - they contian rings of 5 to 7 carbon atoms - examples would be buckminsterfullerene and nanotubes. 

Buckminsterfullerene - C₆₀

• Hard - very strong covalent bonds that are difficult to overcome. 
• Hollow - due to hexagonal shape with give or seven carbon atoms. 
• Low melting and boling points - there are weak forces of attraction between molecules (weak intermolecular forces) that are easy to overcome. 
• Soft and slippery - they are a hexagonal ball shape, therefore can act as a lubricant.

Nanotubes - (Graphene)

• Graphene in a cylinder form.
• The length of a nanotube is very long compared to its width- so nanotubes have high length to diameter ratios - several milimetres long but only a few nanometres wide - high SA:V
• High tensile strength (can resist being stretched).
• Can conduct electricity - one free delocalised electron that can carry charge.

Graphene is a giant covelent structure - an allotrope of carbon.

Graphine is one layer of graphite

It consists only of carbon - one element

Physical properties and links to structure and bonding present:

• 2D - only one atom thick, therefore extremely flexible. 
• Strong - three covalent bonds 
• Good conductor of electricity - there is one unbonded electron which can move throughout the structure and carry charge.
• High melting and boiling points - strong covalent bonds which are difficult to overcome and therefore require a lot of energy.

• High melting and boiling points 

A lot of energy is required to overcome the strong covalent bonds between molecules. 

• Does not conduct electricty 

There are no delocalised electrons or ions so no charge can flow. Molecules have no overall charge. Diamond and silicon dioxide have four bonds - and therefore there are no free electrons, however graphite, and therefore graphene are exceptions to this as they make three bonds to carbon and one carbon is left that can carry charge through the structure. 

• Insoluable in water
• Strong 

Strong and multiple covalent bonds in the structure. 

Nanoscience is the study of particles that have a diameter between 1 - 100 nanometres.

• Nanometres - nm - 0.000000001 - 1 x 10 -9m
• Nanoparticles have different properties to larger sized pieces of the same substances, because they have a much larger to surface are to volume ratio,
• so when we decrease the size of a particle by ten times, we increase the SA:V ratio by ten. 
• Nanoparticles only contain a few hundred atoms, because they have a diameter between 1 - 100 nm.

Coarse Particles (PM10 or dust)

• Diameter of between 1 x 10 -5 m and 2.5 x 10 -6m, and they contain many thousands of atoms. 

Fine Particles (PM2.5 or soot)

• Diameter of between 100-2500 nm ( 1 x 10 -7m and 2.5 x 10 -6m), and contain several thousand atoms

Nanoparticles can be used for:

• Medicine
• Sunblock - better coverage
• Catalyst
• Electronics
• Cosmestics
• Deodrants

Risk of using Nanoparticles

• Nanoparticles could be absorbed into our body and enter our cells - whether this is harmful or not, can be discovered by future studies.