Download ppt - Periodic Trends and Z eff

  • Periodic Trends and ZeffRole of core electron shielding in atomic properties

  • Atomic RadiusAtomic radius is defined as half the distance between neighboring atomsCovalent Radius is half the distance between two bonded atomsvan der Waals radius is half the distance between neighboring atoms in a gas We wont use it in todays discussion.

  • Atomic RadiusAs the Zeff increases, the electrons feels more positive pull towards the nucleus, so the atomic radius decreases across a period.

  • Atomic RadiusAs n increases down a group, the atomic radius increases, but then decreases across a group

  • Ionic RadiusThe ionic radius of an element is the elements share of the distance between neighboring ions in an ionic solid.Generally:Cations are smaller than their parent atomsAnions are larger than their parent atoms

  • Ionic Radius

  • Ionic Radius

  • Ionization EnergyIonization energy is the amount of energy necessary to remove and electron from an element in the gas phaseAn element with a low ionization energy will readily form a cation and usually make good conductors.

  • Ionization EnergyIonization energies increase across a periodZeff is increasing and therefore the electrons are being held more tightlyThe decrease going down a groupElectrons are getting further away from the nucleus

  • First and Second Ionization EnergiesThe second ionization energy is generally significantly higher than the first ionization energyException: Atoms with valence electrons in the ns shell.Look at the Group 1 and Group 2 elements. The second ionization energy for the Group 2 elements is nearly equal to the first. Why?

  • Ionization Energies and Metallic CharacterLow ionization energies account for metallic character of elements in the s, d and f blocks.They readily lose electrons and can therefore exist as a metalic solid

  • Electron AffinityA measure of how much an atom wants an electronA High electron affinity means that energy is released when an element gains an electronA Low or negative electron affinity implies that energy must be supplied to push the electron onto the atom

  • Electron AffinityElectron repulsion effect by adding an electron to an already occupied orbital