Atoms

• Balanced Equation

  When number of atoms on each side is the same
• Balanced Equation

  • H^2+Br^2 —> H^2Br^2
• State symbols

  • Potassium = solid state
  • Water = Liquid state
  • Hydrogen gas state
  • Potassium Hydroxide as state aqueous
• Chromatography

  Separates a mixture of coloured solutes in a solution
• Why can’t sand be filtered from a mixture of sand and salt solution?

  Sand does not dissolve in water, it’s particles are too large to pass through the microscopic holes in a filter paper, and the salt particles are small enough to pass through together with the water particles.
• Why must the sample be higher than the solvent in paper chromatography

  To stop it dissolving in the solvent.
• How to determine the two coloured spots at the same substance?

  They will be the same colour and travel the same distance on the chromatogram.
• Mendeleev's predictions

  Importance to the success of his table
• How scientists today can explain why Mendeleev was correct


  1. When the missing elements were discovered, their properties were found to be similar to his predictions

  2. Protons, neutrons and electrons had not been discovered then and Mendeleev did not know about isotopes

  3. The modern periodic table places elements in order of atomic number

  4. The existence of isotopes means that some elements have higher relative atomic masses than expected from their atomic number alone
• Metals and non-metals in the periodic table

  • Metals are found towards the bottom and left, and non-metals are found towards the top and right
• Mercury is in the liquid state at room temperature
• Hydrogen

  It can form H+ ions and H- ions, which is unusual for a non-metal
• The noble gases have very low boiling points, so they are all in the gas state at room temperature
• There is a gradual change or trend in the noble gases' boiling points going down the group
• Reactions of lithium, sodium and potassium with oxygen

  1. Lithium burns with a red flame, sodium with an orange flame and potassium with a lilac flame

  2. The reactions become more vigorous from lithium to potassium
• Balanced equation for the reaction of lithium with oxygen

  4Li(s) + O2(g) → 2Li₂O(s)
• Molecules

  2 or more atoms, held together by chemical bonds
• Atom


  Protons and neutrons (the nucleus) surrounded by electrons orbiting around the nucleus
• Electrons


  • Always moving in shells
• Protons and Neutrons

  Have same mass
• Neutral atom

  3 protons and 3 electrons, positive and negative charge cancel each other out
• Ion


  Negative and positive (Electrons being lost or gained)
• Positive ion

  More protons than electrons in atom
• Negative ion

  More electrons then protons in atom
• Mass number


  Top number on periodic table
• Atomic number


  Bottom number on periodic table
• Atomic number


  How many protons and electrons
• Mass number


  Total number of Neutrons + Protons
• Protons determine what element an atom will be
• Isotopes


  Different forms of the same element that have the same number of protons, but a different number of neutrons
• Relative Atomic Mass


  Sum of (isotope abundance x isotope mass) / Sum of Abundance of all isotopes
• Chemical formula


  • H2SO4 - 2 hydrogen, 1 sulphur, 4 oxygens
• Molecule


  2 or more atoms bonded
• Compound


  2 elements bonded
• In balancing chemical reactions, you can't change the little numbers, you change the big numbers in front of the periods
• Putting a 2 in front of H20

  Doubles all atoms (2 hydrogens to 4 and 1 oxygen to 2)
• Chemical reaction


  Reactants are mixed together to form products
• Filtration


  • Removes insoluble solids from liquids, usually using filter paper in a filter funnel
• Evaporation


  • Removes soluble solids that have dissolved, by heating the solution to make the solvent disappear and leave behind the crystals
• Crystallisation


  Put evaporating dish in water bath to heat more gently, so thermal decomposition doesn't take place. Crystals form as solids are less soluble at colder temperatures. Filter out and dry the crystals.