4.5.1 Compare and explain the properties of substances resulting from different types of bonding
Melting/Boiling Points
Solubility
Conductivity
Melting/Boiling Points
- bond strength dictates the attractive forces between the particles and thus how high the melting and boiling points are
- however, melting points can be affected by impurities (such as alloys instead of pure metals), which weaken the structure and result in lower melting points
- covalent macromolecular structures have extremely high melting and boiling points
- metal/ionic compounds also have relatively high boiling points due to ionic attractions
- hydrogen bonds are 1/10th the strength of a covalent bond
- London forces are 1/100th the strength of a covalent bond
- the weaker the forces, the more volatile the substance
Solubility
- polar substances tend to dissolve in polar solvents such as water
- non-polar substances dissolve in non-polar solvents, such as heptane
- in organic molecules, the longer the non-polar carbon chain tail, the less soluble in water it is
Conductivity
- free-flowing electrons or ions are required for conductivity
- metals and graphite are excellent conductors
- molten ionic salts also conduct but are chemically decomposed in the process
- in diamond or simple molecules where electrons are held in fixed positions, no conductivity occurs