Periodic Trends in Atomic Properties Effective Nuclear Charge Atomic and Ionic Radii Ionization Energy Electron Affinity Electronegativity

Definitions Effective Nuclear Charge, ENC- charge exerted on the valence electrons as a result of the shielding effect ENC = (Atomic Number) - ( # core electrons) Your author: # core electrons = S = screening constant For Neutral Atoms ENC = # of valence electrons Shielding Effect - shielding by the core electrons effectively reducing the charge exerted on the valence electrons (EACH CORE ELECTRON DIMINISHES THE NUCLEAR CHARGE BY ONE UNIT THAT IS EXERTED ON ALL OF THE VALENCE ELECTRONS) True shielding is less because the valence electrons have small probability of penetrating the core electrons, but NO WORRIES Core electrons- electrons in an inner energy level Valence electrons - electrons in the outermost energy level

Definitions Atomic Radius - distance from the nucleus to the 90% boundary of the outermost valence electrons for the neutral atom Ionic Radius - distance from the nucleus to the 90% boundary of the outermost valence electrons after an atom has gained or lost electrons. Ionization energy - energy required to remove an electron from a neutral atom (Kilojoules/mole) 2nd Ionization energy - energy require to remove an electron from an ion with a +1 charge 3rd Ionization energy - ? Electronegativity- measures the ability of a neutral atom to attract an additional electron (No units, fluorine has a value of 4.0) Electron Affinity - energy absorbed or released when a neutral atom gains an electron (Kilojoules/mole)

Effective Nuclear charge Write the electronic configuration for Al (no noble gas abbreviation) Indicate the # of core electrons and valence electrons for Al. Find the effective nuclear charge for: Al, Na, Cl, Na+, Cl-, Sc, Sc2+, V, V+ Note for neutral atoms ENC = group # for representative elements What is the ENC of transition elements?

List ENC for each group

Consider the trends & periodic table for Effective Nuclear Charge Atomic Radius Ionization Energy Electronegativity Electron Affinity Now look at the experimental data for anomalies & explain!!

Trends in the Atomic Radius

Trends in Atomic Radius

Trends in Ionization Energy

Trends in Ionization Energy

Successive Ionization Energies

Trends in Electron Affinity

Examples of Trends Arrange the following atoms in order of increasing radius Mg, Al, Ca Be, F, I Ionic Radius-Arrange the following in order of increasing radius Cl, Cl-, and Cl+ Na+, Cl-, and Ne (isoelectronic) Ionization Energy Recall Coulomb’s Law F = KQ1Q2/r2 Arrange the following in order of increasing ionization energy

Examples of Trends Multiple Ionization Energies of Mg 1st Ionization Energy 738 KJ/mole 2nd Ionization Energy 1451 KJ/mole 3rd Ionization Energy 7733 KJ/mole Explain why each additional ionization energy is larger. Explain why there is such an increase after the second Ionization energy.