Elements:

• The building blocks of matter
•  Consist of only one type of atom
• Cannotbe broken down chemically into simpler substances.
•  Can exist as individual atoms or they can exist as atoms of the same element bonded together
•  For example, N₂(Nitrogen) is diatomic, thus explaining the (2).
•   Other examples: O₂, Cl₂, F₂, I₂, Br₂

Compounds:
• Pure substances are composed of two or more elements bonded in fixed ratios.
• They cannot be separated using physical methods
• Properties are different from the elements they contain.
• Example:
• H2O, CH4, NaCl, CO2

IMPORTANT: 

Elements and Compounds have an exact melting and boiling point.

General Information:

•  In a metallic bond, the electrons are delocalized, moving freely.
•  An ionic lattice structure cannotconduct electricity in solid form.
•  SiO₂(Silicon Dioxide) is a network covalent giant structure.
•  NH₃(Ammonia) is a simple covalent compound.

Mixtures:

• These are composed of one or more elements or compounds with no fixed ratios.
•  Contain pure substances and are not chemically bonded.
• Can be separated using physical methods.
• The components of the mixture retain their individual properties.

Separation Techniques:
Filtration: Removes an insoluble solid from a liquid or solution.
Steps:
• The mixture is poured through a filter paper held in a filter funnel
• The insoluble solid cannot pass through the filter paper/funnel
• Water can pass through the pores (filter paper/funnel) and be collected in the beaker.
• Used mainly for heterogeneous mixtures.
Evaporation: Separates a mixture that has a solute dissolved in a solvent (usually water)

Steps:
• Heat the solution in an evaporating dish
• Solvent evaporates leaving the solute behind
• Used mainly for homogeneous mixtures.
Solvation:
Steps:
• Separates a heterogeneous mixture of two solids based on their differences in solubility
• One of the substances is soluble in a solvent, and the other is insoluble.
• The solvent molecules (usually water) surround the soluble molecules and dissolve the solid in a solution
• The insoluble solid is then separated by filtration.
• The soluble substance is then separated from the solution by evaporation.

Distillation: Separates a liquid mixture based on the difference in volatility (ability to evaporate) and/or the boiling points.
Steps: Water-Ethanol Experiment used as the example
• Place the water-ethanol mixture in a round bottom flask
• Heat the mixture
• The ethanol will evaporate first (lower boiling point), raise the distillation column, and pass through the condenser.

• It will cool down and then recondense to be recollected in another flask.

Fractional distillation:
Similar to normal distillation, however, it separates the components of crude oil at an oil refinery.
Paper Chromatography: Separates a mixture of solutes in a solvent
GCSE Chemistry – Paper Chromatography #63→GOOD VIDEO TO WATCH IF YOU’RE CONFUSED
Steps:
• Get filter paper and draw a horizontal baseline
• Add a sample of ink onto the baseline
• Place filter paper into a beaker containing a shallow amount of a solvent (making sure not to submerge ink)
• The solvent will seep up the paper and the different dyes in the ink will separate
• If the chemicals aren’t soluble in the solvent then they won’t move up the paper
Mobile phase: a substance that the molecules can move in
Stationary phase: A substance or material that the molecules can’t move in
Recrystallization: Removes impurities mixed with a solid
Steps:
• The impure mixture is dissolved in a hot solvent to make a saturated solution.
• The solution is then cooled, causing the solubility of the dissolved solids to decrease.
• The desired product forms crystals, leaving the impurities behind in the solution.
• The solution is then filtered to obtain the pure product.
• Recrystallization is used to purify sugar crystals from sugar cane juice and is also used by pharmaceutical companies to remove any impurities that could contaminate the medication.