Ch8910 Lec 1

(5/4/20, bes)

Welcome to the last (1/2) week of classes!!!!

I have finished up organizing my gradebook. After this morning's lecture prep, i will go into school and send an email with all of your grades..."grades-so-far." As you are aware, we have a final exam scheduled for Weds, May 13th. This exam is worth 20% of your final grade and will be delivered thru WebAssign. I have not written the exam yet, but i am fairly certain that it will be questions mainly from the past WA questions/chapters, i may have to write/code a few to specifically address some specifics. In the email i will send later this morning, I have included a table with your predicted grade...if your final exam score is a 90%, 70%, 50%, then what is your overall letter grade...so you have an idea of how much effort to put towards this final exam.

With 3 chapter to finish the course (as previously taught), i am going to pick and choose the most important topics from the remaining chapter. I will make reference to textbook figures.

Chapter 8: Periodic Relationships Among the Elements

Chapter 7 ended by discussing electron configuration. This concept is very important for many other issues that arise in chemistry. The electron configuration is what determines the behavior of an element. As Ch8 is titled, there are relationships or trends that exist depending on the electron configuration and the periodic table is organized in a way to highlight these trends:

Atomic size (see Figure 8.5)

- Going down (i.e. Li --> Na --> K, etc) the elements/atoms get bigger...electrons are added to out orbitals/shells...2s, 3s , 4s, etc.

- Going across (i.e. B --> C --> N --> O --> F --> Ne), you might think that the atom would get bigger, but the additional electrons are being added to the same orbital (i.e. 2p) at the same time the # of protons is increasing.

Atomic size of ions (see Figure 8.9)

Cations (i.e. Li+, Na+, K+,etc)

- when compared to the atom, Li (152 pm - picometer)> Li+ (78 pm); cations are smaller than the atom since it lost an electron.

electron configuration of Li = 1s2 2s1, whereas Li+ is just 1s2.

Anions (i.e. F-, Cl-, Br-, etc)

- when compared to the atom, F (72 pm) < F- (133 pm); anions are bigger than the atoms since it has gained an electron.

electron configuration of F is 1s2 2s2 2p5, whereas Cl- is 1s2 2s2 2p6.

General Behavior/Reactivity

Groups or columns (up and down) have similar chemical characteristics. This should make sense because the electron configurations are similar:

- Li (s) is very similar to Na (s), which is also very similar to K (s)...each of these atoms have a "s-orbital" with 1 electron:

- Li --> 1s2 2s1

- Na --> 1s2 2s2 2p6 3s1

- K --> 1s2 2s2 2p6 3s2 3p6 4s1

- F₂ (g) is very similar to Cl₂ (g)...each of these atoms have 5 electrons in the "p-orbital":

- F₂ --> 1s2 2s2 2p5

- Cl₂ --> 1s2 2s2 2p6 3s2 3p5'

LOTS of pretty element pictures in this chapter...please look thru these.

Chapter 9

in lab this afternoon...

Chapter 10

Weds.