1. Drill – 11/19
What is meant by “periodic trend”?

2. Periodic Trends

3. Nuclear Charge
Nuclear charge-the charge in the nucleus or the number of protons
Across – increases
Down – increases

4. Valence Electrons
The electrons in the outermost energy level (s and p orbitals only!)
Across – increase
Na Mg Al Si … Ar
3s1 3s2 3s23p1 3s23p2 …3s23p6

5. Valence Electrons
The electrons in the outer most energy level (s and p orbitals only!)
Down – stays the same. This is why there are trends in reactivity for families
Be Mg Ca Sr
2s2 3s2 4s2 5s2

6. Atomic Mass
Weighted average (based on mass and percent abundance of each naturally occurring isotope)
Across – increases
Down – increases
Remember there are some exceptions to this – like Te and I

7. Shielding Effect
The shielding effect is the reduction of attractive force between the nucleus (+) and its outer electrons (-) due to the blocking affect of the inner electrons
Nucleus
Shielding electrons
Valence electrons ‘shielded’ by inner electrons

8. Shielding Effect Across – stays the same
Electrons are added in the Valence shell and the shielding electrons remain the same

9. Shielding Effect Down – increases
Another layer of electrons is added and the shielding between the valence shell and the nucleus increases

10. Atomic Radius
One half the distance from center to center of like atoms
1/2

11. Atomic Radius Across – decreases
As the number of p+ in the nucleus and e- in the valence shell increases, the nucleus exerts a greater pull on all of the electrons

12. Atomic Radius Down – increases
A new energy level is added increasing the size of the atoms

13. Ionization energy
The amount of energy needed to remove an electron
1st Ionization Energy – energy needed to remove the 1st e- from an atom
+ Ionization
Energy +
+ e-

14. Ionization Energy Across – increases
e- are more strongly attracted to nucleus, increasing the energy necessary to remove an e-

15. Ionization Energy Down – Decreases
e- are further from the nucleus. Less energy is needed to remove an electron.

16. Ionic Radius
Radius of an ion -- the size of an ion is different than the size of the atom it came from.
If an atom loses an e- then it will have a pos. charge and is called a CATION.
If an atom gains an e- then it will have a neg. charge and is called an ANION.

17. Ionic Radius
Cations will be smaller than the original atom. This is due to a stronger nuclear pull.
Anions will be larger than the original atom. The additional e- goes into the same energy level and the e- will repel each other and spread out.

19. Electronegativity
The tendency for an atom to attract electrons in a bond.

20. Electronegativity Across – Increases
Stronger nuclei have greater nuclear pull for e-.

21. Electronegativity
Down – Decreases
Larger atoms have less pull on e-.

22. Electron Affinity
The energy change when an electron is added to a neutral atom to form a negative ion
Higher e- affinity = easier to add an e- = stronger nucleus

23. Trends Across the Periodic Table
Shielding Effect Stays the Same
Atomic Radius decreases
Ionization Energy Increases
Electronegativity Increases
Electron Affinity Increases

24. Trends Down the Periodic Table
Shielding Effect Increases
Atomic Radius Increases
Ionization Energy Decreases
Electronegativity Decreases
Electron Affinity Decreases