1. Decoding the Periodic Table
Periodicity
Decoding the Periodic Table

2. Effective Nuclear Charge
The charge of the nucleus that is felt by the valence electrons
Symbol: Zeff
Zeff = atomic number (Z) - # of core e-
What is the effective nuclear charge for each of the 8 main groups?

3. Effective Nuclear Charge

4. Periodicity Rules In the same period: In the same group:
Zeff increases going to the right
In the same group:
Distance between valence electrons and nucleus increases going down

5. Disclaimer!
Transition metals are the worst…

6. Atomic Radius
The distance from the center of the nucleus to the valence electrons in an atom
When does atomic radius INCREASE in a period?
As Zeff DECREASES (valence electrons are held less tightly)
Moving to the LEFT
When does atomic radius INCREASE in a group?
As distance INCREASES
Moving DOWN

7. Atomic Radius

8. Atomic Radius

9. Electronegativity The ability of a neutral atom to gain an electron
When does electronegativity INCREASE in a period?
As Zeff INCREASES (new valence electron is attracted by a stronger positive charge)
Moving to the RIGHT
When does electronegativity INCREASE in a group?
As distance DECREASES (attractive force is stronger at smaller distances)
Moving UP

10. Electronegativity

11. Electronegativity

12. First Ionization Energy
The energy that it takes to remove one electron from a neutral atom
When does 1st IE INCREASE in a period?
As Zeff INCREASES (electron being removed is held more tightly)
Moving to the RIGHT
When does 1st IE INCREASE in a group?
As distance DECREASES (attractive force is stronger at smaller distances)
Moving UP

13. 1st Ionization Energy

14. 1st IE: Main Groups

15. First Ionization Energy

16. Ionic Radius: Cations
The distance from the center of the nucleus to the valence electrons in a positively charged ion
When does cation radius INCREASE in a period?
As the number of electrons lost DECREASES (remaining electrons are pulled closer to nucleus)
Moving to the LEFT
When does cation radius INCREASE in a group?
As distance INCREASES
Moving DOWN

17. Ionic Radius: Anions
The distance from the center of the nucleus to the valence electrons in a negatively charged ion
When does anion radius INCREASE in a period?
As the number of electrons gained INCREASES (valence electrons held less tightly)
Moving to the LEFT
When does anion radius INCREASE in a group?
As distance INCREASES
Moving DOWN

18. NOTE:
Anions ALWAYS have larger ionic radii than cations!
Why is this?

19. Ionic Radius

20. Ionic Radius

21. Warm-Up
Rank the 4 Periodic Trends from what YOU think is easiest to hardest to understand.
Atomic Radius
Electronegativity
1st Ionization Energy
Ionic Radius