chemistry paper 1

• percentage mass of a compound

  Ar x number of aroms / Mr of compound x 100
• Number of moles


  Mass / Mr
• Volume of gas


  mass of gas / Mr of gas x 24
• concentration


  mass of solute / volume of solute
• concentration


  number of moles of solute / volume of solvent
• Atom economy


  relative formula mass of desired products / relative formula mass of all reactants x 100
• Percentage yield


  actual yield / theoretical yield x 100
• Atoms


  The smallest part of an element that can exist
• Chemical symbols


  Represent an atom of an element e.g. Na represents an atom of sodium
• Compounds


  Formed from elements by chemical reactions, contain two or more elements chemically combined in fixed proportions, can be represented by formulae
• Mixtures


  Consist of two or more elements or compounds not chemically combined together, can be separated by physical processes
• Development of the model of the atom

  1. First thought to be tiny spheres

  2. Plum pudding model (atom is a ball of positive charge with negative electrons embedded in it)

  3. Alpha particle scattering experiment (mass concentrated at centre (nucleus) and nucleus charged)

  4. Bohr's model (electrons orbit nucleus at specific distances)

  5. Later experiments (positive charge subdivided into protons, neutrons discovered)
• Atomic number


  The number of protons in an atom of an element
• Relative charge of subatomic particles

  • Proton (+1)
  • Neutron (0)
  • Electron (-1)
• An atom has an overall charge of 0, so number of protons = number of electrons
• Mass number


  Sum of protons and neutrons in an atom
• Isotopes


  Atoms of the same element with different numbers of neutrons
• Relative atomic mass


  Average value that takes account of the abundance of the isotopes of the element
• Electronic structure


  Electrons occupy the lowest available energy levels (shells closest to nucleus), electronic structure tells you how many electrons are in each shell
• Compounds


  Substances in which 2 or more elements are chemically combined
• Types of strong chemical bonds

  • Ionic
  • Covalent
  • Metallic
• Ionic bonding


  • Particles are oppositely charged ions
  • Occurs in compounds formed from metals combined with non-metals
• Covalent bonding


  • Particles are atoms which share pairs of electrons
  • Occurs in most non-metallic elements and in compounds of non-metals
• Metallic bonding


  • Particles are atoms which share delocalised electrons
  • Occurs in metallic elements and alloys
• Formation of ionic bond

  1. Metal atom loses electrons to become positively charged ion

  2. Non-metal atom gains electrons to become negatively charged ion
• An ion is an atom that has lost or gained electron(s)
• Ionic compounds


  • Giant structure of ions
  • Held together by strong electrostatic forces of attraction between oppositely charged ions
  • Forces act in every direction since the structure is in 3D
• Covalent bonding


  • Atoms share one or more pairs of electrons
• Polymers


  Large covalently bonded molecules
• Giant covalent structures (macromolecules)

  • Consist of many atoms covalently bonded in a lattice structure
  • Examples: diamond, silicon dioxide
• Metallic bonding


  • Positive ions (atoms that have lost electron(s)) and delocalised electrons arranged in a regular pattern
  • Delocalised electrons are free to move through the structure
  • Delocalised electrons are shared through the structure so metallic bonds are strong
• Diamond


  Each carbon is joined to 4 other carbons covalently
• Diamond


  • Very hard
  • Has a very high melting point
  • Does not conduct electricity
• Graphite


  Each carbon is covalently bonded to 3 other carbons, forming layers of hexagonal rings which have no covalent bonds between the layers
• Graphite


  • The layers can slide over each other due to no covalent bonds between the layers, but weak intermolecular forces
  • Soft and slippery
• Graphite

  One electron from each carbon atom is delocalised
• Graphite

  • Similar to metals because of its delocalised electrons
  • Can conduct electricity - unlike Diamond, because the delocalised electrons can move
• Graphene

  Single layer of graphite
• Graphene

  • Has properties that make it useful in electronics and composites
  • Very strong because atoms within its layers are very tightly bonded
  • Elastic because the planes of atoms can flex relatively easily without the atoms breaking apart
• Fullerenes

  Molecules of carbon atoms with hollow shapes