1. Many properties of elements depend on
Electron configuration
How strongly outer electrons (-) are attracted to the nucleus (+)
This attraction is described by Coulomb’s Law which defines the force of attraction (F) between charged particles (Q)

2. Zeff
Core electrons shield or screen valence electrons from the charge of the nucleus
Nuclear charge is not experienced the same by all electrons.
Outer electrons experience it less, so Z is reduced. The new Z is called Zeff
Zeff = Z – S
where Z is actual nuclear charge (#p in nucleus) and S is shielding constant (# core e-)

3. Compare Li to Be to B
Write the electron configuration of Li, Be, and B.
Determine Z, S, and Zeff for each.
What is the trend for Zeff across a period? Explain the trend.

4. As go across, Zeff increases because atomic number increases: more p in nucleus, so Z increases while n and # core e- remains same: S same

5. Compare Ne to Na Write the electron configuration of Na and Ne.
Determine Z, S, and Zeff for each.
What is the trend for Zeff when you start a new period? Explain the trend.

6. As start a new period, Zeff decreases because there are more protons in the nucleus so Z increases (pull inward is stronger) but there are more core electrons so value of S gets closer to value of Z (more shielding so attraction is lower) The two counter balance one another

7. As go down a group, Zeff changes less dramatically than going across period
As you go down, Zeff increases slightly
Bigger cloud is less effective at shielding, so attraction is slightly greater as get bigger

8. Zeff and Periodic Trends
Atomic size
Greatly influences other atomic properties and is critical to understanding element behavior
Ionization energy
Energy to remove electrons
Electron affinity/electronegativity
Energy to add electrons

9. Nonbonding vs. Bonding Atomic Radius
What is Size?
Nonbonding vs. Bonding Atomic Radius
Nonbonding describes atomic radii (atoms)
distance from nucleus to
outer shell cloud
(usually for gas)

10. Bonding Atomic Radius Usually refers to bond length
When 2 atoms bond, they smush together
A-B bond length would be rA + rB
rA in the bond will be slightly less than rA alone because of the smush factor

11. Atoms do not have hard surfaces, so size depends on the atoms near it and bond length might be slightly less than expected

12. What happens to size (atomic radii) as you go
Down a group?
Across a period?
WHY?

13. ↑
Zn vs Ga
Why is Ga > Zn?

14. As go down, n dominates
As you go across, Zeff dominates

15. Some exceptions to trend
Why is Ni smaller than Cu (trend says it should be larger)???
Hint: Has to do with Zeff

16. Size of Ions How does size of cation compare to parent atom? Explain.
M vs. Mn+
How does size of anion compare to parent atom? Explain.
NM vs. NMn-

17. What if isoelectronic?
Compare size of
O F- Na+ Mg2+
K Cl- Ca2+ S2-

18. Ionization Energy Energy to ??? Endo or exo? +∆H or -∆H?
Do all elements have only 1 Eion?
Trend going across a period and down a group?

20. N vs. O
Explain this exception

21. Successive ionization E of Be

23. Electronegativity and e- Affinity
Do you remember what electronegativity is?
What is the trend across a period and down a group?

25. Electron Affinity Energy to ??? Endo or exo? +∆H or -∆H?
Trend going across a period and down a group?

26. Electron Affinity
As go across should get more (-). Why are Be and N (+)?
Compare F to Cl or O to S. Why do they disobey trend?