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• Mixtures are made of 2 or more substances (elements or compounds) that haven't been chemically combined. Mixtures can be separated. Their chemical properties don't change because they have been mixed with another substance. 
• Filtration

  • Separates mixtures of insoluble (can't dissolve) solids and liquids.
  • Done by pouring the mixture through filter paper:
  • The insoluble solid is trapped.
  • The liquid runs through the paper and is collected below.
• Chromatography

  • Separates solutions with a number of different solutes (solids) in the solvent (liquid).
  • Place a drop of the solution to be separated near the bottom of a piece of chromatography paper. Dip the very bottom of the paper into a suitable solvent. The solvent (liquid) moves up the paper and carries the solutes (solids) in the solution with it.
  • Different solutes (solids) move at different speeds, so they separate on the paper.
• Crystallisation

  • Separates solutions into their constituent (different) parts: dissolved solids (solutes) and liquids (solvents).
  • Heat the mixture so that the solvent evaporates.
  • Eventually, crystals of the solute (dissolved solids) will form.
  • We can collect the solvent (liquid) by condensing it as it evaporates.
• In chromatography, the number of spots produced by a mixture can vary depending on which solvent is used.
• • The definition of a chemically pure substance is that it consists of only a single element or compound.
  • This means that pure samples will only ever produce 1 chromatography spot regardless of solvent identity.
• A solvent (mobile phase) is run through the mixture on paper (contains the stationary phase). The substances will move up the paper at different rates. The most soluble substance will move the furthest.
• Rf value

  Rf = distance travelled by substance/ distance travelled by solvent.
• What do we call a pure sample that's run next to the tested substance to see if it's a component in the mixture?

  Reference substance
• The elements are arranged in order of their atomic number (number of protons).
• Elements in the same group have the same number of electrons in their outer shell
• Because all elements in a group have the same number of electrons in their outer shell, they have similar chemical properties. This means they will all react in similar ways.
• Transition metals have: higher melting points, higher density and lower reactivity.
• • Metallic bonding involves an attraction between positively charged ions and negatively charged, delocalised electrons.
  • Metallic bonds are found in metals and alloys (mixtures of metals and other substances).
• Intramolecular forces are forces within molecules.
• Small molecules have weak intermolecular forces. This means that they have low melting and boiling points.
• Intramolecular bonds

  Strong covalent bonds found within small molecules
• Intermolecular forces Weak forces found between small molecules
• The sum of intermolecular forces between smaller molecules is small
• The sum of intermolecular forces between bigger molecules is greater
• Small Covalent Molecules

  • Lower melting/ boiling points
  • Don't conduct electricity
• Large Covalent molecules

  • Higher melting/ boiling points
  • Don't conduct electricity
• Giant Covalent Structure

  Some non-metals form giant structures with atoms joined together by covalent bonds.
• Giant Covalent Structures

  No Specific Formula

  • Giant covalent structures don't have a specific formula because the structure can be any size.
• Giant Covalent Structures

  Very high melting points

  • The strong covalent bonds between atoms make them solids at room temperature.
  • High temperatures and significant energy are required to break the structure's covalent bonds.
• Giant Covalent Structures

  1 large molecule

  • Giant covalent structures exist as 1 large structure or molecule.
  • There are no intermolecular forces because there is only 1 molecule.
• Polymers are large, chain-like molecules that can extend for thousands of atoms. Polymers are held together by:

  • Strong covalent bonds between atoms in molecules.
  • Weak intermolecular forces between molecules.
• Because of the large size of polymer molecules, the intermolecular forces add up to be quite strong.

  • Polymers are usually solid when at room temperature.
  • Many polymers melt easily because the intermolecular forces remain less strong than chemical bonds.
• Polymers are made up of repeating units. Because of this, we can show their chemical structure as a unit that is repeated lots of times.
• Giant covalent structures have very high melting points. This is because the covalent bonds between the atoms are very strong.
• Diamond

  High melting point

  • A lot of energy is needed to break strong covalent bonds.
  • Diamond has lots of strong covalent bonds. This means that it has a high melting point.
• Diamond

  Covalent Bonds

  • Each carbon atom in diamond is bonded to 4 other carbon atoms by strong covalent bonds.
  • This creates a giant covalent structure.
• Diamond

  Does not conduct electricity

  • Diamond does not conduct electricity because there are no delocalised electrons in the diamond structure.
• Diamond

  Hard

  • There are lots of strong covalent bonds in diamond. This makes it very hard.
  • Because diamond is hard, it is used as a cutting tool to cut other materials.
• Graphite

  Soft

  • The carbon atoms form layers of hexagonal (6-sided) rings, with weak intermolecular forces keeping the layers together.
  • The layers can easily slide over one another, so graphite is very soft.
  • This makes graphite useful as a lubricant and as pencil ‘lead’.
• Graphite

  Covalent Bonds

  • Each carbon atom in graphite is bonded to 3 other carbon atoms by strong covalent bonds.
  • This creates a giant covalent structure.
• Graphite

  Conducts Electricity

  • Each carbon atom forms 3 bonds.
  • This means that there is 1 delocalised electron from every carbon atom.
  • This electron can move freely, so graphite is a good electrical conductor.
• How many other carbon atoms is each carbon atom in diamond bonded to?

  Four
• Diamond cannot conduct electricity as there are no delocalised electrons in its structure.
• Graphene

  Conducts Electricity

  • Each carbon atom has a delocalised electron.
  • Graphene is a single layer of graphite so it also conducts electricity because of the carbon atoms’ delocalised electrons.