S2.4 Models to materials

Question 1

what do bonding triangles show?

Answer 1

there’s a continuum from one type of bonding to the other 2 so idea of purely ionic or covalent is an oversimplification

Question 2

general rules of the bonding triangle

Answer 2

small difference in electronegativity+low average negative electronegativity=metallic; small difference in electronegativity+high average electronegativity=covalent; large difference in electronegativity+mid range average electronegativity=ionic

Question 3

disadvantage of using bonding triangles

Answer 3

don’t predict properties of transition metals or their compounds well

Question 4

what is thermoplastic, what is their structure and give 2 ex

Answer 4

individual chains with intermolecular forces, it can be repeatedly heated and cooled and remoulded into different shapes; bc intermolecular forces are partially overcome when heated and form again when polymer cools eg polyethene and PVC

Question 5

desirable properties of plastics(5)

Answer 5

strength and durability, flexibility, lack of reactivity, thermal insulation, electrical insulation

Question 6

which plastics are strong, rigid and hardwearing?

Answer 6

HDPE(high density polyethene), PVC, nylon and perspex

Question 7

which plastics are flexible?

Answer 7

LDPE, plasticised PVC are easily rolled into sheets/films and can be used as cling film

Question 8

why are plastics unreactive?

Answer 8

addition polymers have unreactive, saturated C—C bonds and inert side groups, polyethene containers used for storage of corrosive substances eg hydrofluoric acid which reacts with glass

Question 9

which plastics have good thermal insulation?

Answer 9

polypropene, polyethene, polystyrene have high SHCs and v low thermal conductivity so excellent thermal insulators

Question 10

which plastics are good electrical insulators?

Answer 10

PVC and used as a covering for electrical wires

Question 11

what is a thermosetting polymer, give structure and examples

Answer 11

polymers with extensive cross-linking(covalent bonds) cannot be remoulded eg Bakelite and polyurethanes or naturally=cross-link chains in collagen

Question 12

what does it mean when plastics are amorphous?

Answer 12

completely random structure with chains arranged like in a plate of spaghetti

Question 13

what does it mean when plastics are semi-crystalline?

Answer 13

contain some regions where the chains are more ordered and packed more closely together and some amorphous regions

Question 14

which factors determine how strong a plastic is?

Answer 14

length of chain(relative molecular mass), degree of branching and arrangement of groups on chain

Question 15

which structure of polymers tend to be stronger and why?

Answer 15

polymers with longer chains and less branching bc there are stronger London forces between chains

Question 16

what does less branching in polymers lead to?

Answer 16

a more crystalline polymer and stronger and stiffer material

Question 17

describe the structure in LDPE

Answer 17

contains high proportion of branching, highly branched polymer chains are less able to pack closely together so contact points between chains are reduced, therefore weaker London forces, weak intermolecular forces=more flexible and lower tensile strength

Question 18

what is tensile strength?

Answer 18

how well a material resists a stretching force without breaking

Question 19

describe bonding and structure in HDPE

Answer 19

virtually no branching, lack of branching=polymer chains pack more tightly in a more regular arrangement-structure is more crystalline and higher density, more efficient chain packing increases strength of London forces so chains held more tightly, makes polymer stiffer and increases its tensile strength

Question 20

draw diagram of branching in LDPE and HDPE

Question 21

what is both LDPE and HDPE usually used for?

Answer 21

LDPE=plastic bags bc more flexible; HDPE=packing crates bc more rigid

Question 22

draw bonding in Kevlar(show H bonds)

Question 23

what is nylon and kevlar used for and what type of bonding do they have?

Answer 23

both used for making ropes and kevlar used for body armour; both have strong intermolecular hydrogen bonds along whole chain

Question 24

which polymers are generally transparent?

Answer 24

amorphous polymers but semi-crystalline usually translucent

Question 25

why is light scattered in polymers?

Answer 25

bc of the differences in density between different regions in semi-crystalline polymers

Question 26

what is a plasticiser and what does it do?

Answer 26

molecules that insert themselves between the polymer chains forcing them apart so reducing the strength of the intermolecular forces between them which allows chains to move more freely. some polymers PVC can be made more flexible using this

Question 27

explain how structure links to flexibility

Answer 27

branching usually increases flexibility bc forces between chains are reduced; cross-linking decreases flexibility bc covalent bonds between chains means they’re less able to move relative to each other

Question 28

why is polyethene not susceptible to attack by acids?

Answer 28

bc it’s non-polar and has strong non-polar C—C bonds throughout

Question 29

what makes condensation polymers more likely to be biodegradable?

Answer 29

susceptibility to hydrolysis

Question 30

what conditions are needed for ethene molecules to produce polyethene?

Answer 30

200 degrees and 2000 atm or small amount of O2 or organic peroxide

Question 31

how are esters formed?

Answer 31

condensation reaction from a carboxylic acid and alcohol

Question 32

what is PET or PETE used for?

Answer 32

in manufacturing of plastic bottles for drinks and fibres for clothing

Question 33

how is a polyamide formed?

Answer 33

condensation reaction dicarboxylic acid reacts with a diamine(2 NH2 groups) so monomers linked by amide group

Question 34

how to work out the repeating units of polyesters and polyamides from monomer structures

Question 35

how do biological macromolecules form and break down?

Answer 35

form by condensation polymerisation and break down by hydrolysis