electronic configurations of atoms

• thompson - early atomic structure 


  used a cathode ray tubes to determine the ratio of electric charge to the mass of an individual electron
• mass of an individual electron

  -1.76 x 10^8 C/g
• early atomic structure - thompson 


  plum pudding model
• gold foil - rutherford


  discovery of protons
• photoelectric effect - einstein

  demonstrated that light has not only wave but particle properties
• uncertainty principle - heisenberg

  you never know both the momentum (mass x velocity) and the position of an electron
• Pauli exclusion principle 


  no more than 2 electrons can occupy an orbital, must have opposite spin
• Aufbau principle 


  electrons fill the lowest available energy first
• Hunds rule 


  with orbitals of equal energy, electrons fill the orbitals singly before filling in pairs
• valence electron 


  outermost electrons
• cation 


  an ion with a net positive charge
• anion 


  an ion with a net negative charge
• Mendeleev's periodic table 


  organised in order of increasing atomic mass
• group I and group VII

  most reactive elements
• attraction between positive nucleus and valence electrons depends on :

  number of protons in the nucleus, shielding effect of other electrons closer to nucleus, distance from the nucleus
• effective nuclear charge 


  the nuclear charge felt by an electron when both the actual nuclear charge and the shielding of of the other electrons are taken into account
• effective nuclear charge increase by...

  moving from left to right
• atomic radius going across a period

  atomic radius decreases
• atomic radius going down a group

  atomic radius increases
• atomic radius of anion

  ionic radius increases
• radius of a cation

  ionic radius decreases
• ionisation energy 


  the minimum energy required to remove an electron from an isolated atom
• ionisation energy going across a period

  ionisation energy increases
• ionisation energy going down a group

  ionisation energy decreases
• electron affinity 


  the negative of the energy change that occurs when an electron is accepted by an atom in the gaseous state to form an anion
• electronegativity 


  the ability of an atom to attract towards itself the electrons in a chemical bond