Chemistry p1

• Substances are made of atoms
• 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)
• If there's no number after a symbol, there's an invisible 1
• 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 a mixture


  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)
• State symbols


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


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


  • Protons and electrons have equal and opposite charges (+1 and -1)
  • Neutrons have no charge (0)
• Atomic number


  Number of protons in the nucleus
• Mass number


  Number of protons and neutrons in the nucleus
• Isotopes


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


  Percentage of each isotope in a sample
• Average relative atomic mass

  Calculated from the relative abundances of isotopes
• Development of the periodic table

  • Ordered by atomic weight, then grouped by properties (Mendeleev)
  • Gaps predicted and later filled by new discoveries
• Electron configuration


  Arrangement of electrons in shells/orbitals around the nucleus
• Periodic table sections


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


  Column in the periodic table, indicates number of outer shell electrons
• 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 or empty outer shells, very unreactive
• Ion


  Atom that has gained or lost electrons, no longer neutral
• Ion charges


  • Group 1 - 1+
  • Group 2 - 2+
  • Group 7 - 1-
  • Group 6 - 2-
  • Transition metals - variable
• Ionic bonding


  • Metal atoms donate electrons, non-metal atoms accept them
  • Ionic compounds have high melting/boiling points, can conduct electricity when molten or in solution
• Metallic bonding


  Metal atoms form a lattice with delocalized electrons around them
• Covalent bonding


  • Non-metal atoms share electrons to fill outer shells
  • Simple molecular structures have low melting/boiling points, cannot conduct electricity
• Giant covalent structures


  • Atoms form continuous networks of covalent bonds, very high melting/boiling points
• Surface area to volume ratio

  Increases as particle size decreases
• Mole


  A specific number of atoms/molecules, used to compare amounts of substances