Understanding Points
Structure 2.4.1—Bonding is best described as a continuum between the ionic, covalent and metallic models, and can be represented by a bonding triangle.
Structure 2.4.2—The position of a compound in the bonding triangle is determined by the relative contributions of the three bonding types to the overall bond.
Structure 2.4.3—Alloys are mixtures of a metal and other metals or non-metals. They have
enhanced properties.
Structure 2.4.4—Polymers are large molecules, or macromolecules, made from repeating subunits called monomers.
Structure 2.4.5—Addition polymers form by the breaking of a double bond in each monomer.
Bonding triangle (Van Arkel-Ketelaar diagram)
•
Shows the degree of covalent, ionic, or metallic character in a compound
•
•
Alloys
1.
A mixture of one metal with another or a non-metallic element
2.
Ions of different size scattered throughout lattice disrupting the network of +ve and delocalised electrons
3.
Distinct properties due to different packing of cations in the lattice
4.
Chemically stable
5.
Stronger: less ductile and less malleable than pure metals
6.
Resistant to corrosion
Alloy | Component | Usage |
Steel | Iron + carbon + other | Construction |
Brass | Copper + zinc | Plumbing |
Duraluminium | Aluminium + copper + manganese | Aircraft |
Bronze | Copper + tin | Electrical wiring |
Figure 4.5.3. Applying a force on a pure metal versus on an alloy
Polymers
•
Consist of many repeating units (monomers) joined together
•
The longer the chain length, the higher the strength and melting point
1.
Thermoplastic: made from alkenes, soften when heated and harden when cooled
2.
Thermosetting: change irreversibly so cannot be remoulded once shaped
3.
Elastomers: flexible, change back into original form when stress removed, e.g. rubber
Addition polymers