C3 Structure and Bonding

C3.1 States of matter

• Solid:
• Particles are packed closely
• Vibrate in fixed positions
• Liquid:
• Particles are close together
• Can slip and slide over each other randomly
• Gas:
• Particles have a lot of space between them
• Zoom around randomly
• When melting and boiling, energies transferred from the surroundings to the substance
• The simple particle models of solid, liquids and gases are useful but has limitations as the atoms, molecules and ions that make up all substances are not solid spheres with no forces between them
• 
• Caption: Heating curve

C3.2 Atoms into Ions

• Elements react together to form compounds by gaining or losing electrons or by sharing electrons
• The elements in group 1 react with the elements in group 7
• Group 1 each lose one electron to gain a stable electronic structure
• This electon is given to an atom from Group 7 which gives them a stable electronic structure
• 
• Caption: Dot and cross diagrams

C3.3 Ionic Bonding

• Ionic compounds are held together by strong forces of attraction between their oppositely charged ions
• The strong electrostatic forces of attraction is called ionic bonding
• They are arranged in a giant structure
• 
• Caption: dot and cross diagram of alcium chloride

C3.4 Giant ionic structures

• It takes a lot of energy to break the many strong ionic bonds that hold a giant lattice together
• High melting points
• All solids at room temperature
• Ionic compounds conduct electricity when molten or dissolved in water
• Their ions can be mobile and carry charge through the liquid
• 
• Caption: Ionic compounds

C3.5 Covalent Bonding

• Covalent bonds are formed when atoms of non-metals share pairs of electrons with each other
• Each shared pair of electrons is a covalent bond
• Many substances containing covalent bonds consist of simple molecules but some have giant covalent structures
• 
• Caption: Covalent bond dot and cross diagrams

C3.6 Structure of Simple Molecules

• Substances made up of simple molecules have low melting and boiling points
• The intermolecular forces are weak but the intramolecular forces (covalent bonds) are strong
• Only the weak intermolecular forces need to be broken when melting
• Simple molecules carry no charge
• They do not conduct electricity
• 
• Caption: Intermolecular and intramolecular forces

C3.7 Giant Covalent Structures

• Some covalently bonded substances have giant structures and have very high melting and boiling points
• The strong covalent bonds need to be broken when melting
• They are all insoluble in water
• Hard and don't conduct electricity, except graphite
• Graphite contains layers of covalently bonded carbon atoms
• No covalent bonds between the layers
• They slip and slide over each other
• It is soft and slippery
• Can conduct electricity as there are delocalised electrons between the layers
• Diamond has a rigid giant covalent structure
• It is very hard
• 
• Caption: Structure of diamond, graphite and C60 fullerene

C3.8 Fullerenes and graphene

• As well as diamond and graphite, carbon also exists as fullerenes, which can form large cage like structures and tubes, based on hexagonal rings of carbon atoms, although they may also appear in rings of five or seven
• The fullerenes are finding uses as a transport mechanism for drugs to specific sites in the body, as catalysts and as reinforcement for composite materials
• Graphene is a single layer of graphite and so is just one atom thick. Its properties, such as its excellent electrical conductivity, will help create new developments in the electronics industry in the future
• 
• Caption: Examples of fullerenes, nanotubes and graphene

C3.9 Bonding in metals

• The atoms in metals are closely packed together and arranged in regular layers
• You can think of metallic bonding as positively charged metal ions which are held together by electrons from the outermost shell of each metal atom.
• These delocalised electrons are free to move througout the fiant metallic lattice
• The strong electrostatic attraction between the negatively charged electrons and the positively charged ions bond the metal ions to each other
• 
• Caption: Metallic bonding

C3.10 Giant metallic structures

• Metals can be bent and shaped because the layers of atoms (or positively charged ions) can slide over each other
• Alloys are harder than pure metals because the regular layers in a pure metal are distorted by atoms of different sizes in an alloy
• Delocalised electrons in metals enable electricity and thermal energy to be transferred through a metal easily
• Metals have high melting points because it takes a lot of energy to separate the metal ions from their fixed positions and break down the lattice to melt the metal
• 
• Caption: Alloy

C3.11 Nanoparticles

• Nanoscience is the study of small particles that are between 1 and 100 nanometres in size (a few hundred atoms)
• Nanoparticles may have properties different from those for the same materials in bulk. This is because nanoparticles have a high surface area to volume ratio with a high percentage of their atoms exposed at the surface
• Nanoparticles may result in smaller quantities of materials such as catalysts being needed for industrial processes

C3.12 Applications of nanoparticles

• New developments in nanoparticulate materials are very exciting and could improve many aspects of modern life
• The increased use of nanoparticles needs more research into possible issues that might arise in terms of health and the environment
• Their large surface are a to volume is useful as a catalyst but this also makes them dangerous as if there is a spark near a large quantity of nanoparticles, there could be a violent explosion
• Breathing in tiny particles could damage the lungs and they could enter the bloodstrean through the lungs
• Could affect aquatic life by accumulating in organisms over time