Chemistry paper 1

• Element


  A type of atom represented in the periodic table by a symbol
• Compound


  A substance that contains two or more different types of atoms chemically bonded together
• Compound


  • Water (H2O)
• Chemical reaction


  Atoms change what they're bonded to and how they're bonded
• Ways to represent a chemical reaction

  • Word equation
  • Chemical equation using symbols
• Balancing a chemical equation

  1. Start with atoms only in compounds

  2. Balance atoms that are only on one side

  3. Use numbers in front of elements/compounds to multiply
• Atoms are not created or destroyed in a chemical reaction, the same number of each type of atom must be on both sides
• Mixture


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


  1. Filtration (for large insoluble particles)

  2. Crystallization (evaporate solvent to leave solute)

  3. Distillation (heat solution, cool gas to condense liquid)
• Physical processes


  • No new substances are being made
• States of matter


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


  Require energy (usually heat) to overcome electrostatic forces of attraction between particles
• Melting and evaporation are physical changes, not chemical reactions (no chemical bonds are broken)
• Atomic models


  • JJ Thompson: plum pudding model (positive charge with electrons)
  • Rutherford: nucleus with electrons orbiting (mostly empty space)
  • Bohr: electrons in shells/orbitals
  • Chadwick: nucleus contains protons and neutrons
• Protons, electrons, neutrons


  • Protons: positive charge, mass 1
  • Electrons: negative charge, mass 0
  • Neutrons: no charge, mass 1
• Periodic table


  • Bottom number: atomic number (protons)
  • Top number: mass number (protons + neutrons)
• Isotopes


  Atoms of the same element with different numbers of neutrons
• Relative abundance


  Percentage of each isotope in a sample
• Average relative atomic mass is calculated by adding up the masses of all isotopes and dividing by 100
• Development of the periodic table

  • Ordered by atomic weight, then grouped by properties (Mendeleev)
  • Gaps predicted, later filled as new elements discovered
• Electron configuration


  Electrons fill up shells/orbitals around the nucleus
• Electron shell filling order

  • 1st shell: max 2
  • 2nd and 3rd shells: max 8
  • 4th shell: max 2
• Metals, nonmetals, metalloids


  • Metals (left of staircase): donate electrons
  • Nonmetals (right of staircase): accept electrons
  • Metalloids (on staircase): have properties in between
• Group


  Column in periodic table, indicates number of electrons in outer shell
• Group names


  • Group 1: alkali metals
  • Group 7: halogens
  • Group 0: noble gases
• Alkali metals


  • Have 1 electron in outer shell, readily donate it
  • Reactivity increases down the group
• Halogens


  • Have 7 electrons in outer shell, readily accept 1 more
  • Reactivity decreases down the group
• Noble gases


  • Have full outer shells, very unreactive
• Ion


  Atom that has gained or lost electrons, no longer neutral
• Transition metals


  • Can form ions with different charges
• Metallic bonding


  Metal atoms bonded in a lattice with delocalized electrons
• Metallic properties


  • Good conductors of electricity and heat
• Ionic bonding


  Metal atoms donate electrons to nonmetal atoms to form ions
• Drawing ionic bonding


  1. Use dot and cross diagrams to show electron transfer

  2. Ions must have charges that add up to zero in a compound
• Ionic compounds


  • Consist of lattice of ions, have high melting/boiling points, can conduct electricity when molten or in solution
• Covalent bonding


  Nonmetal atoms share electrons to fill outer shells
• Simple covalent molecules


  • Cl2, N2, H2O, CH4
• Simple molecular structures


  • Have relatively low boiling points, cannot conduct electricity
• Giant covalent structures


  Atoms form continuous networks of covalent bonds, e.g. diamond, graphite