Chemistry

• Atom


  Made up of protons, neutrons and electrons
• Proton


  • Positive charge
• Electron


  • Negative charge
• Neutron


  • Neutral, no charge
• Period


  Goes left and right on the periodic table
• Group


  Goes up and down on the periodic table
• Period


  Depicts how many shells there are
• Schrodinger model


  Most accurate model of the atom
• We can predict a lot of things about an atom using the periodic table
• Atomic number


  Amount of protons an atom has
• Atomic mass


  Protons + neutrons
• Relative atomic mass


  Average mass of the element
• Predicting maximum electrons in a shell

  2n^2 (2 x 1^2 = 2, 2 x 2^2 = 8, 2 x 3^2 = 18, 2 x 4^2 = 32, etc.)
• AMU


  Atomic Mass Unit
• Proton


  • 1 AMU, +1 charge
• Neutron


  • 1 AMU, 0 charge
• Electron


  • 0 AMU, -1 charge
• Neutrons and protons have mass relative to each other but electrons weigh so little that it is considered to have no weight
• Core charge


  Effect of protons on valence electrons, calculated as protons - non-valence electrons
• Blanket effect


  More electrons between nucleus and valence electrons means more interference and less tightly held valence electrons, making bigger elements more unstable
• Atomic radius


  Distance from nucleus to outer shell
• Electronegativity

  How much an element wants an electron, increases right and up on periodic table (excluding noble gases)
• First ionisation energy


  Energy to remove an electron, follows same trends as electronegativity
• Mendeleev was the creator of the first periodic table
• Electrons

  Arranged into 'groups' that hold electrons
• Groups of electrons

  • Each group is in a different location usually getting progressively further away from the nucleus
  • The largest of these groups are called the shell
• Schrödinger model

  Breaks down the shells into further groups (sub-shell) rather than the Bohr model
• Electrons

  • Orbit the nucleus in shells
  • As they get further away from the nucleus they can hold more electrons
• Predicting the maximum amount of electrons in a shell

  Use the rule 2n^2
• Electron shell capacity

  • 1 shell: 2 electrons
  • 2 shell: 8 electrons
  • 3 shell: 18 electrons
• Atoms and electrons will always exist in the most "natural" or stable form
• Predicting the number of electrons

  Fill from the shell closest to the nucleus working way out when each shell is full
• The Bohr model only works up until 18 electrons, so we must use the Schrödinger model to predict any more
• Shielding effect

  The blocking of the positive charge from the nucleus by inner-shell electrons
• Shielding effect

  • Increases when there are more shells between the valence and the nucleus
  • Increases going down a group but doesn't change across a period
• Core charge

  A measure of the nuclear charge 'experienced' by valence shell electrons
• Core charge

  Increases going across a period but doesn't change going down a group
• Core charge

  Protons - inner electrons
• Periods go left to right, groups up and down
• Shielding effect

  The 'blocking' or 'cancelling' of the nucleus' charge by inner-shell electrons