Presentation on theme: "Periodic Trends and Zeff"— Presentation transcript:
1Periodic Trends and Zeff Role of core electron shielding in atomic properties
2Atomic 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 gasWe won’t use it in today’s discussion.
3Atomic RadiusAs the Zeff increases, the electrons feels more positive ‘pull’ towards the nucleus, so the atomic radius decreases across a period.
4Atomic RadiusAs n increases down a group, the atomic radius increases, but then decreases across a group
5Ionic RadiusThe ionic radius of an element is the element’s 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
8Ionization 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.
9Ionization Energy Ionization energies increase across a period Zeff is increasing and therefore the electrons are being held more tightlyThe decrease going down a groupElectrons are getting further away from the nucleus
10First and Second Ionization Energies The 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?
11Ionization Energies and Metallic Character Low 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
12Electron Affinity A measure of how much an atom ‘wants’ an electron A 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
13Electron AffinityElectron repulsion effect by adding an electron to an already occupied orbital