GCSE SCIENECE CHEM AQA

• This is good for higher and Foundation Tier double combined Trilogy and triple separate chemistry that's topics 1 to five atoms bonding quantitative chemistry and chemical and energy changes
• Substances are made of atoms, the different types of atoms are represented in the periodic table by a symbol
• Compound


  A substance that contains two or more different types of atoms chemically bonded together
• Atoms change what they're bonded to and how they're bonded through chemical reactions
• Word equation


  A representation of a chemical reaction using words
• Chemical equation


  A representation of a chemical reaction using symbols
• Atoms are not created or destroyed in any chemical reaction, there must be the same number of each type of atom on both sides
• Balancing a chemical equation

  1. Start balancing atoms that are only in compounds

  2. Balance carbons first

  3. Balance hydrogens

  4. Use numbers in front of elements or compounds to multiply them up

  5. Finish balancing the element that has no knock-on effect
• Mixture


  Any combination of any different types of elements and compounds that aren't chemically bonded together
• Solution


  A mixture of a solute (solid dissolved in a liquid) and a solvent (the liquid)
• Separating a mixture


  1. Filtration (for large insoluble particles)

  2. Crystallization (to leave a solute behind after evaporating the solvent)

  3. Distillation (to separate liquids with different boiling points)
• These are all physical processes and not chemical reactions because no new substances are being made
• States of matter


  • Solid (particles vibrate around fixed positions)
  • Liquid (particles are still touching but free to move past each other)
  • Gas (particles are far apart and move randomly)
• Gases can be compressed, while solids and liquids cannot
• Melting and evaporation


  Require supplying energy, usually in the form of heat, to overcome the electrostatic forces of attraction between the particles
• Melting and evaporation are physical changes, not chemical reactions, as no chemical bonds are broken
• Atom model development


  • JJ Thompson's plum pudding model
  • Rutherford's discovery of the small, dense nucleus and mostly empty space
  • Bohr's discovery of electron shells/orbitals
  • Chadwick's discovery of neutrons
• Protons, electrons, neutrons


  • Protons and electrons have equal and opposite charges of +1 and -1 respectively, neutrons have a charge of 0
  • Protons and neutrons have a relative mass of 1, electrons have a very small mass
• Periodic table information


  • Atomic number = number of protons
  • Mass number = number of protons + neutrons
  • Isotopes = atoms of the same element with different numbers of neutrons
• The periodic table was originally ordered by atomic weight, then later reorganized by Mendeleev based on chemical properties
• Electron configuration


  Electrons fill up shells/orbitals around the nucleus, with a maximum of 2, 8, 8, 2 electrons in each successive shell
• Periodic table sections


  • Metals (left of staircase)
  • Non-metals (right of staircase)
  • Transition metals
• Group


  The column an atom is in on the periodic table, indicates the number of electrons in the outer shell
• Group names


  • Group 1 - Alkali metals
  • Group 7 - Halogens
  • Group 0 - Noble gases
• Reactivity trends


  • Alkali metals become more reactive down the group as the outer electron is further from the nucleus
  • Halogens become less reactive down the group as the outer shell is further from the nucleus
• Ion formation


  • Metals form positive ions by losing electrons
  • Non-metals form negative ions by gaining electrons
• Ionic bonding


  Formed between a metal and a non-metal, where the metal donates electrons to the non-metal
• Metallic bonding


  Formed between metal atoms, with a lattice of positive ions and delocalized electrons
• Covalent bonding


  Formed between non-metals, where atoms share electrons to fill their outer shells
• Molecular ions


  Consist of a group of atoms bonded together and carrying an overall charge
• Ionic compound names


  Consist of the positive metal ion name followed by the negative non-metal ion name
• Simple molecular/covalent structures


  Individual molecules with relatively low boiling points due to weak intermolecular forces
• Giant covalent structures


  Continuous networks of atoms bonded together, such as diamond and graphite, with high melting/boiling points
• Allotropes


  Different structural forms of the same element, e.g. diamond and graphite are allotropes of carbon
• Nanoparticles


  Structures between 100-2500 nm in size, have a high surface area to volume ratio
• The total mass of substances is conserved in a chemical reaction
• Mole


  A specific number of atoms or molecules used to compare amounts of substances
• The atoms that go in must come out in a chemical reaction, so we must balance equations
• Relative formula mass


  The sum of the relative atomic masses of the atoms in a compound
• Some reactions produce a gas product which, if it leaves the reaction vessel, will result in a seeming decrease in mass of the reactants