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
(protons) & (levels)

2. Nuclear Charge & Shielding
protons(+) attracting e–’s(–)
shielding:
inner e– levels block nuclear charge
decreases Ne Li
across a period
+10 +3
What happens to atomic radius? Na Ar
down a group
increases
+11
+18
WHY?

3. 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)

4. Ions & Ionic Radius Cations from metals: e–’s removed
positive (+) charge
smaller
outer shell lost
Anions from nonmetals:
e–’s added
negative (–) charge
larger
more e– repulsions

5. WHY? Quick Quiz! Atoms get ________ down a ________. bigger, period
smaller, group
bigger, group
smaller, period
WHY?
more energy levels
more shielding
less attraction

6. WHY? Quick Quiz. Atomic radii _________ across a period? get bigger
get smaller
stay the same size
are weird
WHY?
more protons
more nuclear charge
more attraction

7. Quick Quiz.
Which of the following correctly orders atomic size from largest to smallest?
F > Cl > Br
Li > Na > K
F > N > B
Mg > Al > S

8. Quick Quiz.
Metals tend to ________ electrons to form _________ cations.
gain, positive
gain, negative
lose, negative
lose, positive

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

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

11. Periodic Trends (Summary)
ATTRACTION INcreases
so…Atomic Radius __________
decreases
so…Ionization Energy _________
increases
so…Electronegativity _________
increases
ATTRACTION DEcreases
so…Electronegativity _________
so…Ionization Energy _________
so…Atomic Radius __________
All explained by ATTRACTION:
nuclear charge
shielding
increases
decreases
decreases

12. (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)

13. Quick Quiz.
Which of the following is the most electronegative? Cl Se Na I

14. 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.

15. 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 lower
nuclear charges.
D. halogens are smaller with fewer protons.

16. 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)