1. nuclear charge & shielding
Periodic Trends
We will explain observed trends in
Atomic (and Ionic) Radius
Ionization Energy
Electronegativity
size
lose e–
attract e–
explained by:
nuclear charge & shielding
more protons
more attraction
more levels
less attraction

2. decreases across period
Atomic Radius
decreases across period
-more protons/nuclear charge
(more attraction)
-more levels of
shielding
(less attraction)
increases down group
Note: covalent or metallic radius of bonded atoms vs. van der Waals radius of nonbonded atoms (Noble Gases)

3. increases across period
Ionization Energy (IE): +
energy required to remove an e–
increases across period
-more protons/nuclear charge
(more attraction)
-more levels of
shielding
(less attraction)
decreases down a group

4. Electronegativity (EN) Trends
atom’s ability to attract bonded electrons
increases across period
-more protons/nuclear charge
(more attraction)
-more levels of
shielding
(less attraction)
decreases down group

5. Periodic Trends (Summary)
ATTRACTION INcreases
(more protons)
so…Atomic Radius __________
DEcreases
so…Ionization Energy _________
INcreases
so…Electronegativity _________
INcreases
ATTRACTION DEcreases
so…Electronegativity _________
All explained by ATTRACTION:
so…Ionization Energy _________
so…Atomic Radius __________
nuclear charge (protons)
shielding (levels)
(more levels)
INcreases
DEcreases
DEcreases

6. (same energy level/shielding)
Quick Quiz!
As you go across period 3 from Mg to Cl, the energy needed to remove an electron from an atom ______________.
A. generally increases
B. generally decreases
C. does not change
D. varies unpredictably.
WHY?
more protons
more nuclear charge
more attraction
(same energy level/shielding)

7. Quick Quiz.
Of the following, which is the most electronegative? Cl Se Na I

8. Quick Quiz.
The noble gases have _____________.
A. high ionization energies.
B. high electronegativities.
C. large atomic radii.
D. a tendency to form both cations and anions.

9. Quick Quiz.
Alkali metals have lower ionization energies than halogens because _______________.
A. alkali metals are smaller with more protons.
B. halogens are larger with more protons.
alkali metals are larger with fewer protons.
D. halogens are smaller with fewer protons.

10. Quick Quiz.
Fluorine is the most electronegative halogen because it is ___________________.
A. larger with more energy levels (shielding)
B. smaller with more energy levels (shielding)
C. smaller with fewer energy levels (shielding)
D. larger with fewer energy levels (shielding)