Summary

• Substances are made of atoms
• Element


  Different types of atoms represented in the periodic table by a symbol
• Compound


  Substance that contains two or more different types of atoms chemically bonded together
• If there's no number after a symbol there's an invisible one
• Atoms change what they're bonded to and how they're bonded through chemical reactions
• Word equation


  Representation of a reaction using words
• Chemical equation


  Representation of a 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 chemical equations


  1. Start with atoms only in compounds

  2. Balance atoms that are only in compounds

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

  4. Put numbers in front of elements or compounds to multiply them up
• Mixture


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


  Mixture of a solute (solid dissolved in a liquid) and a solvent (the liquid)
• Separating mixtures


  1. Filtration (for large insoluble particles)

  2. Crystallization (evaporate solvent to leave solute)

  3. Distillation (heat solution, cool gas to condense liquid)
• These are all physical processes, not chemical reactions, as 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, most energy)
• 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 broken)
• State symbols


  s for solid, l for liquid, g for gas, aq for aqueous (dissolved in water)
• Atomic models


  • JJ Thompson's plum pudding model (atom as positive charge with electrons)
  • Rutherford's nuclear model (positive charge in tiny nucleus, electrons orbit far away)
  • Bohr's model (electrons in shells/orbitals)
• Chadwick discovered the neutron (neutral charge in nucleus)
• Protons, neutrons, electrons

  • Protons and neutrons have mass of 1, electrons have negligible mass
  • Protons and electrons have equal and opposite charges (+1 and -1 respectively)
  • Neutrons have no charge
• Periodic table


  • Bottom number is atomic number (protons)
  • Top number is mass number or relative atomic mass (protons + neutrons)
• Isotopes


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


  Percentage of each isotope in a sample
• Periodic table was developed by grouping elements based on properties, not just atomic weight order
• Electron configuration


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


  • 1st shell max 2
  • 2nd and 3rd shells max 8
  • 4th shell max 2
• Transition metals have more complex electron configurations
• Metals


  Elements to the left of the staircase on the periodic table, donate electrons to gain full outer shells
• Nonmetals


  Elements to the right of the staircase on the periodic table, accept electrons to gain full outer shells
• Group


  Column an atom is in on the 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 as outer electron is further from nucleus
• Halogens


  • Have 7 electrons in outer shell, readily accept 1 more
  • Reactivity decreases down the group as outer shell is further from nucleus
• Noble gases


  • Have full outer shells, very unreactive
• Ion


  Atom that has gained or lost electrons, becomes positively or negatively charged
• Ion charges


  • Group 1 - 1+
  • Group 2 - 2+
  • Group 7 - 1-
  • Group 6 - 2-
• Transition metals


  • Can form ions with different charges, e.g. Fe2+ or Fe3+
• Metallic bonding


  Metal atoms bonded in a lattice with delocalized electrons
• Properties of metals


  • Good conductors of electricity and heat