Text of Periodic Trends and Z eff Role of core electron shielding in atomic properties
Slide 1
Periodic Trends and Z eff Role of core electron shielding in
atomic properties
Slide 2
Atomic Radius Atomic radius is defined as half the distance
between neighboring atoms Covalent Radius is half the distance
between two bonded atoms van der Waals radius is half the distance
between neighboring atoms in a gas We wont use it in todays
discussion.
Slide 3
Atomic Radius As the Z eff increases, the electrons feels more
positive pull towards the nucleus, so the atomic radius decreases
across a period.
Slide 4
Atomic Radius As n increases down a group, the atomic radius
increases, but then decreases across a group
Slide 5
Ionic Radius The 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 atoms Anions are
larger than their parent atoms
Slide 6
Ionic Radius
Slide 7
Slide 8
Ionization Energy Ionization energy is the amount of energy
necessary to remove and electron from an element in the gas phase
An element with a low ionization energy will readily form a cation
and usually make good conductors.
Slide 9
Ionization Energy Ionization energies increase across a period
Z eff is increasing and therefore the electrons are being held more
tightly The decrease going down a group Electrons are getting
further away from the nucleus
Slide 10
First and Second Ionization Energies The second ionization
energy is generally significantly higher than the first ionization
energy Exception: 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?
Slide 11
Ionization 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
Slide 12
Electron 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 electron A Low or negative electron
affinity implies that energy must be supplied to push the electron
onto the atom
Slide 13
Electron Affinity Electron repulsion effect by adding an
electron to an already occupied orbital
