Topic 1 - Atoms

• Element: a substance containing only one type of atom
• Compound: a substance containing two or more type of atoms chemically bonded together
• Mixture: different substances not chemically bonded
• Due to conservation of mass, atoms can't be created or destroyed so chemical equations have to be balanced
• Filtration removes large, insoluble particles from a liquid
• Evaporation leaves behind crystals of a dissolved substance if heated gently
• Distillation involves condensing the evaporated solvent and collecting it
• Fractional distillation can separate liquids due to their different boiling points
• Chromatography causes substances to rise up the paper due to capillary action - based on substance's solubility
• Solids:

  • Particles in regular arrangement (lattice)
  • vibrate in fixed positions
  • cannot be compressed
• Liquids:

  • particles have no regular arrangement
  • particles able to move past each other
  • cannot be compressed
• Gas:

  • particles are far apart
  • move randomly at high speeds
  • can be compressed
• Physical change = no new substances made
• JJ Thompson created the Plum Pudding model in 1904

  Positive charge with little electrons dotted in it
• Ernest Rutherford discovered the nucleus and how the atom was mostly empty space in 1911 through his gold leaf experiment
• Neils Bohr discovered electron orbited the nucleus in shells
• James Chadwick determined that the nucleus must contain neutrons as well as protons
• Relative Charges:

  • Proton = 1
  • Neutron = 0
  • Electron = -1
• Relative Mass:

  • Proton = 1
  • Neutron = 1
  • Electron = very small
• Mass number is the number of protons and neutrons in a nucleus
• Atomic Number is the number of protons in an element's nucleus
• Atoms have the same amount of protons and electrons so they have a balanced charge - otherwise they are an ion
• Isotopes: same element but different number of neutrons
• Elements were originally ordered based on their atomic weight and some were based on similar properties
• Dimitri Mendeleev based the periodic table on properties (atomic weight had some consideration) and left gaps in it for undiscovered elements in 1954
• Electrons fill up in the order 2,8,8,2
• Metals always donate electrons to have an empty outer shell so become a positive ion
• Transition metals can form multiple ions
• Non-metals always accept electrons to fill their outer shell so they always become a negative ion
• Alkali Metals:

  • Group 1
  • Lose/donate their singular outer electron (1+)
  • Get more reactive down the group as the electron is further away from the nucleus and the force of attraction is less
• Halogens:

  • Group 7
  • Accept a singular electron to fill the outer shell (1-)
  • Get less reactive down the group
  • Boiling point increases further down the group as well
• Noble Gases:

  • Very unreactive as they already have a full outer shell