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

2. 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

3. 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)

4. 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?

5. List ENC for each group

6. 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!!

7. Trends in the Atomic Radius

8. Trends in Atomic Radius

9. Trends in Ionization Energy

10. Trends in Ionization Energy

11. Successive Ionization Energies

12. Trends in Electron Affinity

13. 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

14. 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.