1. Periodic Trends Objectives: AHSGE Reading 4.3 Discern organizational patterns. Other AOD C.3.2 Recognize periodic trends of elements, including the number of valence electrons, atomic size, and reactivity.

2. Atomic Radius Electron clouds surrounding the nucleus (do, do not) have a clearly defined boundary. Atomic size is defined by how closely an atom lies to a neighboring atom, so the size of the atom varies some from one interaction to another.

3. Atomic Radius (continued) Trends across periods: Atomic radius tends to DECREASE as you move across a period. Reason: Increase in positive charge of the nucleus, while adding electrons (e - s) to the same principal energy level. This means no increasing distance b/t e - s and p + s, so p + s pull e - s closer.

4. Trends within groups: Atomic radius tends to INCREASE as you move down a group. Reason: Nuclear charge still increases as p+ s are added, but electrons are added to higher energy levels. Because these e - s are located further from the nucleus, with more e - s b/t it and the nucleus, the positive charge of the nucleus has less “pull” on them. Atomic Radius (continued)

5. Ionic Radius Define ion. Def: an atom, or bonded group, with a positive or negative charge. This happens with the gain or loss of an e -. What is the charge on an electron? What will the charge be if an atom GAINS an e - ? What will the charge be if an atom LOSES an e - ?

6. Ionic Radius(continued) Look at the diagram of a Na atom on the board? What would happen to its size if we remove the outermost valence e - ? 2 Reasons for its decrease in size: 1.It lost its complete outermost orbital. 2.Electrostatic repulsion b/t the remaining e - s decreases, allowing them to be pulled closer together and closer to the nucleus.

7. Ionic Radius(continued) Look at the diagram of a Cl atom on the board? What would happen to its size if we add another outermost valence e - ? Reason for its increase in size: –Electrostatic repulsion b/t the remaining e - s increases, making them move further apart from each other.

8. Ionic Radius(continued) Trends within periods: 1.Groups 1A-4A, and group B elements form smaller positive ions. 2.Groups 3A-8A form larger negative ions. 3.Positive ions get smaller going left-to-right. 4.Negative ions start out larger, but get smaller going from group 5A-8A.

9. Ionic Radius(continued) Trends within groups: Higher energy levels = larger ionic radius