C2: Elements, Compounds, and Mixtures

C2: Elements, Compounds, and Mixtures

1. Purity and Separating mixtures

   • Relative formula mass
     • The total mass of a molecule when all of the relative atomic masses of each atom in the molecule is added together
   • Empirical formula
     • The simplest formula for a molecule
   • Pure and impure substances
     • A pure substance is a substance made up of only one type of element or molecule
   • Filtration
     • The act of filtering a mixture of a liquid or solution and an insoluble solid to collect the solid
   • Crystalisation
     • The act of heating a solution to evaporate the solvent and collect the solute
   • Simple distilation
     • The act of heating a mixture of liquids to collect the liquid with the lowest boiling temperature
   • Fractional distilation
     • The act of heating a mixture of liquids and collecting them all using a fractionating column
   • Chromatography
     • The act of using a solvent to move the chemicals in a mixture to identify the chemicals in the mixture
     • Rf value
       • A value assigned to each chemical to identify it during chromatography
   • Checking purity
     • To check the purity of a substance you can either use chromatography on it or you can check its melting/boiling point against known values

2. Bonding

   • Metals and non-metals
     • Most chemicals on the periodic table are metals
     • Metals and non-metals have certain characteristics that can be used to identify if a substance is either a metal or a non-metal if there is no periodic table avaliable
   • Electronic structure
     • The periodic table is arranged into groups (horizontal rows) and periods (vertical columns)
     • Each period represents the number of electrons in the atoms outer shell and each group represents the number of occupied electron shells
   • Forming ions
     • Ions are formed by an atom either gaining electrons from a bond or losing electrons in a bond
   • Ionic Compunds
     • Ionic compounds can only be formed between metals and non-metals where the non-metal loses electrons and forms a negative ion and the metal gains electrons and forms a positive ion
     • The oppositely charged ions attract each other and form a bond
   • Simple Molecules
     • Covalent bonds are formed between two non-metals where they share electrons to form complete outer shells
   • Giant covalent structures
     • A giant covalent structure is made up of many non-metals and contain many covalent bonds
   • Polymer molecules
     • Polymers are long chain molecules that are made up of repeating units called monomers
   • Structure of metals
     • Metals are formed by many metal ions coming together. They are held together by the 'sea' of delocalised electrons
   • Development of the periodic table
     • Dmitri Mendeleev created the periodic table by grouping elements with similar masses together as well as the elements that reacted similarly
   • Atomic structure and the periodic table
     • The periodic table allows us to identify the structure of atoms by their location on the table

3. Properties of materials

   • Carbon
     • Carbon forms many different compounds since it can bond with either three or all four of its outer electrons
   • Changing state
     • A substance changes state when it melts, boils, condenses, freezes or undergoes sublimation (changing from a solid to a gas and vice vesa)
   • Bulk properties of materials
     • Some substances have different properties to others due to the way the atoms in it are bonded
   • Nanoparticles
     • Nanoparticles have many uses such as titanium oxide nanoparticles in sunscreen