Atoms

• Substances are made of atoms
• The different types or elements 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
• For every one oxygen atom in water, there are two hydrogen atoms
• If there's no number after a symbol, there's an invisible 1
• Atoms change what they're bonded to and how they're bonded through chemical reactions
• Word equation


  A way to represent a chemical reaction using words
• Chemical equation


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

  1. Start with atoms that are only in compounds

  2. Balance the number of atoms on each side

  3. Use numbers in front of elements or compounds to multiply them up
• Mixture


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


  1. Filtration (for large insoluble particles)

  2. Crystallization (to leave a solute behind after evaporation)

  3. Distillation (to separate liquids with different boiling points)
• Physical processes


  • Do not create new substances, just separate existing ones
• 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 energy, usually in the form of heat, to overcome the electrostatic forces of attraction between particles
• Melting and evaporation are physical changes, not chemical reactions, as no new substances are being made
• State symbols


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


  • J.J. Thomson's plum pudding model (positive charge with electrons dotted around)
  • Rutherford's model (positive nucleus with electrons orbiting relatively far away)
  • Bohr's model (electrons in shells or orbitals)
• Chadwick discovered that the nucleus contains neutral charges, which he called neutrons
• Protons, electrons, neutrons


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


  • Bottom number is atomic number (number of protons)
  • Top number is mass number or relative atomic mass (protons + neutrons)
  • Isotopes are atoms of the same element with different numbers of neutrons
• The periodic table was originally ordered by atomic weight, then later grouped by properties
• Electron configuration


  Electrons fill up shells around the nucleus, with a maximum of 2, 8, 8, 2 in the first four shells
• Metals and non-metals


  • Metals are to the left of the staircase on the periodic table, they donate electrons
  • Non-metals are to the right of the staircase, they accept electrons
• Groups on the periodic table

  • Group 1 (alkali metals)
  • Group 2 (alkaline earth metals)
  • Group 7 (halogens)
  • Group 0 (noble gases)
• Alkali metals


  • Have one electron in their outer shell, which they readily donate
  • Reactivity increases down the group as the outer electron is further from the nucleus
• Halogens


  • Have seven electrons in their outer shell, so they readily accept one more to fill it
  • Reactivity decreases down the group as the outer shell is further from the nucleus
• Noble gases


  • Have a full or empty outer shell, so they are very unreactive
• Ion


  An atom that has gained or lost electrons, so it is no longer neutral
• Ion charges


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


  • Can form ions with different numbers of electrons donated
  • Generally harder and less reactive than alkali metals
  • Form colored compounds