Periodic Table Trends

• Valence electrons


  The electrons in the outermost shell of an atom
• Octet Rule


  The tendency for atoms to gain or lose or share electrons in order to achieve a full outer shell of electrons
• Ion


  An atom or compound which has gained or lost electrons and consequently has a positive or negative charge
• Bohr Model of the Atom


  • Electrons orbit around the nucleus in fixed circular orbits
  • The orbits correspond to fixed energy levels (shells)
  • Electrons can only occupy these fixed energy levels and not between two energy levels
  • The further away the electrons orbit the higher the energy level of the shell (to move up a shell an electron must gain energy and to move down a shell an electron must emit or lose energy)
• Emission Spectrum


  The specific wavelengths of light emitted by atoms when electrons in transition from high back to low energy levels releasing specific quantities of light (photons) which sometimes can be seen as visible light
• These spectra act like fingerprints to uniquely identify the presence of any given element
• Emission vs Absorption Spectrum
• Arrangement of the Periodic Table
• Electron Configuration


  Write the EC for Calcium
• Atom vs. Ion


  The electron configuration of an atom will change when it becomes an ion as it seeks to obtain a full outer shell of electrons (the octet rule)
• Electrostatic attraction


  The attraction between the positively charged nucleus of an atom and the negatively charged electrons surrounding it
• Core charge


  The measure of the attractive force felt by the valence electrons towards the nucleus
• Trend in the attraction between Valence electrons and their nucleus

  As you go down a group and left to right across a period
• Ionisation Energy


  The energy required to remove one electron from an atom of an element in the gas phase
• Ionisation Energy


  Closely linked to "Metallic character" whereby the more readily the an atom loses it's valence electron the more metallic in nature it will appear to be
• Successive Ionisation Energies
• Electronegativity


  The strength of which electrons are pulled towards the nucleus of an atom (essentially the oppositive to ionisation energy)
• Flame Tests
• Atomic Absorption Spectroscopy (AAS)


  1. The sample is dissolved in a solvent and is placed in the container

  2. With the help of fuel and oxidant in the presence of a mixer, the sample solution is sprayed on to the flame

  3. The neutral atoms in the flame absorb light radiation from the cathode lamp. The unabsorbed radiation is recorded by the detector
• Applications (uses) of Atomic Absorption Spectroscopy


  • Quantitative analysis of metal elements in water, soil, plant material, and ceramics
  • Analysis of ionic metal elements in blood, saliva, urine samples (sodium, potassium, magnesium, calcium, and zinc)
  • Determination of heavy metals like iron, manganese, copper, zinc, mercury, lead, nickel, in urine and blood
  • Determination of metal elements like copper, nickel, and zinc in the food industry
  • Estimation of Lead in petroleum products
  • Determination of metal concentrations in groundwater and bore well samplings before using for drinking and irrigation