Annoucements
Chapter 7
WebAssign review for the midterm is now up. Begin early. It is long, but it is good exam practice and it is an important part of your second marking period grade.
Work on the chapter 8 portion of your webassign first.
Please look at chapter eight on the Chang Online Learning Center. Go through the Essential Study Partner partial pressures at some point before returning from Thanksgiving.
Upcoming Asssignments
Assignment 1: 1-6, 11, 27, 36 on webassign.
Assignment 2:
Remember the trends:
Atomic radius-- one half the distance between two identical nuclei.
- Group trend: Within a group atomic radius increases as the atomic number increases (elements at the bottom of a group have a larger atomic radius than at the top)
- Reason: 1. Elements lower in the group have valence electrons with a higher principle quantum number (n) and these orbitals are larger and electrons are consequently further from the nucleus.
- Reason 2. Elements at the bottom of the group have more inner shell (core) electrons that shield the valence (outer shell) electrons from the attraction from the positive nucleus.
- Period Trend: Elements decrease in atomic radius across a period from left to right.
- Reason. The number of inner shell electrons and therefore the shielding remains constant with the addition of each successive electron. The nuclear charge (no of protons) increases with each successive element, so the additional proton causes the valence electrons to experience more attraction to the nucleus.
Ionic Radius--the radius of an element's most common ion.
- Group trend: Increases down a group for the same reason as atomic radius.
- Period trend: Decreases left to right for the same reason as atomic radius. When the ion becomes negative, however, the radius increases dramatically, because valence electrons are now in the next energy level. For example,
| Na+ |
Mg2+ |
Al3+ |
Si |
P3- |
S2- |
Cl- |
| [He]2s22p6 |
[He]2s22p6 |
[He]2s22p6 |
N/A |
[Ne]3s23p6 |
[Ne]3s23p6 |
[Ne]3s23p6 |
| 11 protons |
12 protons |
13 protons |
N/A |
15 protons |
16 protons |
17 protons |
| 10 electrons |
10 electrons |
10 electrons |
N/A |
18 electrons |
18 electrons |
18 electrons |
| 95 pm |
65 pm |
50 pm |
N/A |
large |
184 pm |
181 pm |
- The sodium, magnesium and aluminum ion are isoelectronic, but the aluminum ion has a higher nuclear charge (13 protons) so it is smaller. The phosphide ion has valence electrons in the third (n = 3) energy level, so it is much larger than the cations in period three. The sulfide ion is smaller than the phosphide ion because each has an inner core of 10 electrons so shielding is similar for each, but the sulfide ion has one more positive charge in the nucleus, and the attractive force of this additional proton pulls the valence electrons closer to the nucleus.
