Drill – 11/19

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 • 1 2 3 4 ... 8

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 • 2 2 2 2

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. 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 Shielding Effect 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. One half the distance from center to center of like atoms Atomic Radius 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. The amount of energy needed to remove an electron 1st Ionization Energy – energy needed to remove the 1st e- from an atom Ionization energy + 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