GCSE chemistry paper 1

• Balancing chemical equations


  1. Start balancing atoms that are only in compounds

  2. Can't change small numbers as that would change the compound

  3. Put numbers in front of elements or compounds to multiply them up

  4. Finish balancing elements that are not in compounds
• Mixture


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


  A mixture of a solute dissolved in a solvent
• Separating mixtures


  1. Filtration for large insoluble particles

  2. Crystallization to leave solute behind after evaporating solvent

  3. Distillation to separate liquids with different boiling points
• Physical changes


  • No new substances are being made
  • Breaking intermolecular forces, not chemical bonds
• States of matter


  • Solid - particles vibrate in fixed positions
  • Liquid - particles can move past each other
  • Gas - particles move randomly and have high energy
• Gases can be compressed, solids and liquids cannot
• To melt or evaporate a substance, energy must be supplied to overcome intermolecular forces
• Atom models


  • Plum pudding model - positive charge with electrons dotted around
  • Nuclear model - positive nucleus with electrons orbiting relatively far away
• Atomic structure


  • Protons - positive charge, mass of 1
  • Electrons - negative charge, negligible mass
  • Neutrons - no charge, mass of 1
• Periodic table


  • Atomic number - number of protons
  • Mass number - number of protons and neutrons
  • Isotopes - atoms of the same element with different numbers of neutrons
• Periodic table was developed by grouping elements based on their properties, not just atomic weight
• Electron configuration


  Electrons fill up shells around the nucleus in a specific order
• Periodic table sections


  • Metals - to the left of the staircase
  • Non-metals - to the right of the staircase
• Group


  Column in the periodic table that tells you how many electrons are in the outer shell
• Group properties


  • Group 1 (alkali metals) - readily donate 1 electron
  • Group 7 (halogens) - readily accept 1 electron
  • Group 0 (noble gases) - very unreactive
• Ion


  An atom that has gained or lost electrons, no longer electrically neutral
• Ionic bonding


  Metal atoms donate electrons to non-metal atoms to form a lattice of ions
• Covalent bonding


  Non-metal atoms share electrons to fill their outer shells
• Molecular ions


  Ions formed from a group of atoms, not just a single atom
• Salt


  Any ionic compound, not just sodium chloride
• Ionic compounds


  • High melting/boiling points due to strong intermolecular forces
  • Can conduct electricity when molten or dissolved
• Covalent compounds


  • Relatively low melting/boiling points due to weak intermolecular forces
  • Cannot conduct electricity
• Giant covalent structures


  Continuous networks of covalent bonds, e.g. diamond and graphite
• Allotropes are different structural forms of the same element, e.g. diamond and graphite
• Nanoparticles are between 100-2500 nm in size, smaller than dust particles
• Total mass is conserved in chemical reactions, atoms are not created or destroyed
• Relative formula mass


  Sum of the relative atomic masses of the atoms in a compound
• Mole


  A specific number of atoms or molecules, used to compare amounts of substances
• Mass is conserved in a chemical reaction
• Atoms that go in must come out, so we must balance equations
• Relative atomic mass (RAM)


  The mass of an atom relative to the mass of a carbon-12 atom
• Relative formula mass (RFM)


  The sum of the relative atomic masses of the atoms in a compound
• Reactions can produce a gas product, which can result in a seeming decrease in mass of the reactants
• If you have as many grams of a substance as its relative atomic or formula mass, you have one mole
• Moles


  Calculated as mass (g) divided by relative atomic/formula mass
• Balancing a chemical equation

  1. Determine the number of moles of each reactant and product

  2. Ensure the number of moles of each element is the same on both sides
• Calculating mass of product from mass of reactant

  1. Convert mass of reactant to moles

  2. Use stoichiometry to find moles of product

  3. Convert moles of product to mass
• Stoichiometry refers to the ratio of moles of substances in a balanced chemical equation
• Concentration of a solution can be expressed in moles per decimeter cubed