Structure 2.4 Flashcards
Alloy properties
Lower melting points, less malleable/ductile, harder, less directional bonding
Alloys
A mixture of more than one metal
Polymer
A repeating chain of monomers held together by covalent bonds
Monomer
Individual repeating units in a polymer
Monomers joint in addition reactions
Addition polymer and condensation reactions - don’t form byproducts
Thermoplastics
Soften when heated and harden when cooled, recyclable
Thermosetting plastics
Change irreversibly into hardened thermosets and cannot be recycled
Elastomers
Polymers that are flexible and can be reformed under a force but will return to the original shape when stress is released
Bonding triangle
Shows the three extreme types of bonding plotted against the difference in electronegativity and the change in electronegativity
Ionic bond
Electrostatic attractions between two oppositely charged ions
Covalent bond
The electrostatic attraction between the nuclei of two atoms and their valence electrons, sharing of electrons
Metallic bonds
The electrostatic attraction between the cations and sea of delocalised valence electrons
When does a solid melt?
When attractive forces between particles are overcome and particles are free to move
What is melting point influenced by?
The way in which particles pack in the solid state
Ionic compounds conductivity
Don’t conduct in solid state but conduct when molten or in aqueous liquid
Why do ionic compounds (molten/in aqeous) decompose when conducting?
As conductivity is due to movement of electrons
Conductivity of allotropes of non metals
Usually good as they have delocalised electrons
Elasticity
The ability of a material to resist a distorting influence and return to original when force is removed
Metals elasticity
Elastic as atoms can easily slide over each other in the lattice
Polymer elasticity
Can be stretched without being permanently broken so are elastic
Covalent solid brittleness
Very brittle as bonds cannot be reformed once broken
Metals brittleness
Very malleable as layers of atoms can slide over each other
Ionic solid brittleness
Very brittle as ionic lattice breaks without being deformed when sufficient force is applied
Addition polymers
Formed from alkenes and no other product are produced, a carbon to carbon double bond is broken
100% atom economy
All reactant becomes product
Condensation reaction
Water will be produced in addition to the condensation product
What is needed to form a condensation polymer?
Two functional groups (can be same or different) so that once the condensation product in formed, it can continue reacting with two functional groups
Ester link
One monomer has two carboxlic acid groups, one monomer has two alcohol groups (-COOH, -OH)
Polyester
A polyester is made by a reaction involving an acid with two carboxlic groups, and an alcohol with two alcohol groups.
What happens when a monomer with two carboxylix acid and one monomer with two amine groups react?
A polyamide is formed
Aminde link
When a monomer with two carboxylix acid and one monomer with two amine group react, an aminde link forms (-COOH, -NH2)
Polyamide can also be formed…
By condensing amines with either dicarboxlyic acids or with diacyl chlorides
Kevlar
Condensation polymer and also example of a polyamide
Why is kevlar so strong?
Because it consists of rigid rod shaped molecules that are cross linked by intramolecular hydrogen bonding between the chains
When does kevlar lose its protective properties?
In concentrated sulfric acid solution, the O and N atoms in the amide linkage become prononated and break down
Biological macromolecules
Condensation polymers
Amino acids
Building blocks of proteins, have a carboxyl group and an amino group bonded to the same carbon atom
Peptide bond
Amide bond amino acids form
Polysaccharides
Many sugar units condensed together
Hydrolysis
Reverse reaction of condensation
Alloy
Mixture of more than one metal
Properties of an alloy
Lower melting point, harder, more brittle
What can polymers form and how?
Addition polymers through addition reactions, condensation polymers and polysaccardies through condensation reactions
Thermoplastics
Can be remoulded when heated
Thermosetting
Changes irreversibly in soft solid/viscous state
Elastomers
Flexible polymers that can return to original shape
Delocalised pi electron
An electron shared between two or more nuclei, found in all resonance structures
