Structure and Properties

• Electrostatic forces hold the ions together in an ionic compound
• It takes a lot of energy to break up a giant ionic lattice, there are lots of strong ionic bonds to break
• Have to overcome electrostatic forces of attraction
• Means ionic compounds have high melting and boiling points
• Once enough energy has been supplied to seperate ions from the lattice they are free to move around
• This is when an ionic solid melts and becomes a liquid, ions are free to move anywhere
• Can carry an electrical charge (carry it because can move freely)
• A solid ionic compound cannot carry electricity because they cannot move around
• Many ionic compounds dissolve in water, the water splits up the lattice, ions can move freely, will conduct electricity

Covalently bonded subsatnces usually have a low boiling and melting points

• Means many of the substances are liquids or gases at room temperature

•  Covalent bonds are very strong, atoms within each molecule are held tightly together
• HOWEVER, each molecule is quite seperate from its neighbouring molecule
• Attraction between individual molecules in a covalent substance is relatively small
• Weak intermolecular forces between molecules, overcoming these forces does not require much energy
• Simple molecules have no overall charge so they cannot conduct electricity

• Giant covalent structure: form huge networks of atoms held together by covalent bonds
•  They are very hard, high melting and boiling points, and insoluble in water

Graphite

• Graphite carbon atoms are only bonded to three other carbon atoms so they form hexagons which are arranged in giant layers
• NO COVALENT BONDS BETWEEN THE LAYERS, so the layers slide over eachother easily
• e.g. like sliding a deck of cards
• weak intermolecular forces between layers in graphite, so slide over easily
• Carbon has four electrons in its outer shell, three are joined up so it leaves one spare
• This electron is free to move along the layers of carbon atoms (delocalised electron) so can conduct electricity

• Carbon atoms join together to make large cages which have all sorts of shapes
• Built up of hexagonal rings of carbon atoms
• Can place other molecules in carbon atoms, so could deliver drugs to certain parts of the body

• Can hammer and bend metals into different shapes because atoms in pure metals can slide over eachother easliy
• Alloys are mixtures of metals, so different size atoms in an alloy
• Makes it more difficult for layers to slide over eachother
• Alloys are harder

Properties of metals

• Positive ions in a metal's giant structure are held together by a sea of delocalised electrons
• Electrons are a bit like glue; their negative charge between the positively charged ions holds the ions in position
• Electrons can move around the whole lattice though, because they move and hold metal ions together, the lattice will distort
• Delocalised electrons means they are good conductors of heat and electricity

• When you heat these alloys up, they return to their original shape
• They 'remember' their old shape
• e.g. dentists make braces to move teeth back

Properties depend on:

• monomers used to make it
• conditions reaction is carried out

Different reaction conditions:

• Two types of poly(ethene); high density and low density
• High pressure and a trace of oxygen forms LD ethene, polymer chains are branched and they cant pack closely together

• A catalyst at 50'C and a slightly raised pressure makes HD ethene. They make straighter poly(ethene) molecules and can pack more closely together (stronger than LD)

Thermosoftening polymers

• Soften or melt easily when heated
• Cool back to original shape
• Made up of individual polymer chains tangled together

Thermosetting polymers

• Not soften when heated but will char eventually
• They have strong covalent bonds forming 'cross links' between polymer chains
• Monomers make covalent bonds between polymer chains
• The bonds stops the polymer from softening

• Atoms in polymer chains are held together by strong covalent bonds
• The size of the forces between polymer molecules can be different

• In thermosoftening, the forces between the polymer chains are weak, when we heat the polymer the weak intermolecular forces break
• When it cools, the intermolecular forces bring the polymer molecules back together

• The study of small particles that are between 1 and 100 nanometres in size
• 1 nanometre = 10-9 metres
• Nanoparticles behave differently to the materials they are made from on a larger scale

Uses:

• Cosmetics, the nanoparticles go deeper into the skin so uses include creams, sun tan creams and deodrants
• Delivery of drugs in a nanoparticle cage, so the drug goes to where it needs to

Possible risks:

• Large surface area could make them dangerous, a spark could cause an explosion
• If they are used more and more they may go into the air around us and breathing them in would damage the lungs