chem modelsofparticulatenatureofmatter
Structure 1.1.1 - elements are the primary constituents of matter, which cannot be chemically broken down into simpler substances.
compounds consist of atoms of different elements chemically bonded together in a fixed ratio
mixtures contain more than one element or compound in no fixed ratio, which are not chemically bonded and so can be separated by physical methods
elements:
- primary constituents of matter, cannot be broken down into simpler substances
- denoted by chemical symbol
- defined by the number of protons in the nucleus
compounds:
- atoms consisting of different elements chemically bonded in a fixed ratio
- denoted by chemical formula
mixtures:
- consist of more than one element or compound in no fixed ratio, not chemically bonded
- can be separated through physical methods
solvation, filtration, recrystallisation, evaporation, distillation, chromatography
homogenous:
- uniform composition and properties
- the inter-particle attraction within the different components must be similar in nature to those between the components in the mixture
e.g. air, metal alloys*, dissolved salts
heterogenous:
- non-uniform composition, properties
- interaction between components are different in nature
- i.e. water (hydrogen bonding) and oil (dispersion forces)
separating mixtures
if components in a mixture have distinct difference in a physical property, they can be separated easily
technique chosen will depend upon this property
solubility → solvation, filtration, recrystallisation
boiling point → distillation/evaporation
magnetism → magnet
polarity/adsorption → chromatography
filtration:
- filtrate: what goes through
- residue: what’s left on the membrane
(fractional) distillation:
- when solvent and solute have different boiling points
- difference in polarity → adsorption/desorption
challenge questions:
- If you add
of water to of water, you get of water. Similarly, if you add of ethanol to of ethanol, you get of ethanol. Explain why the volume of solution formed between of water and of ethanol is less than .
The molecules of ethanol can partly fit between the spaces between the water molecules and vice versa.
- Does a mixture have the same classification at all scales?
A mixture may appear homogenous when observed with the naked eye, but may be heterogenous under a microscope. The classification depends on the scale on which the components are analysed.