Announcements:-During Unit 5, we will take 6 quizzes and be able to drop the lowest score.
-We took quiz #1 today.
-We will take quiz #2 tomorrow.
-We received pages 9-15 today.
Homework: Finish pages 9-15
Class: Today, we started off by doing a quick question and answer about what material was going to be on the quiz. After this, we then took our first quiz of unit 5. Once everyone had finished the quiz, Mr. Paek showed us what the answers were and went over them with us. The quiz was out of 8 total points with each question being worth half of a point.
We then started going over pages 9-15.
Page 9: This first page was Guidelines for Drawing Lewis Structures. What you first must do when you are drawing the Lewis Structures is to count the total number of valence electrons in the compound. If you are finding the structure of an ion, remember to add electrons for a negative charge and subtract electrons for a positive charge. Secondly, you should predict the arrangement of the atoms in the molecule, drawing a line to represent a single bond between each pair of bonded electrons. Thirdly, you should find the number of valence electrons left over after forming single bonds. The fourth step is to place electrons around the outside atoms until each is surrounded by eight electrons (the octet rule). H is the only element which does not follow the octet rule. The final step is to place any left over electrons around the central atom.
Page 10: Lewis Structures 1
-Ex: What is the Lewis Structure for CH4
Ans: What you would do would be to find out the needed electrons, how many electrons the compound has, how many electrons are shared, and how many bonds there are. In this instance there are 8 electrons needed for C. There are also 8 electrons needed for H4 because H needs 2 electrons and since there are 4 of the H electrons that makes 8. If you add 8+8 you will get 16. Therefore this compound needs 16 atoms. Next, is the amount of electrons they have. H4 has 4 electrons combined, and C has 4 electrons. That gives you 8 more electrons for 16. Therefore, they have 8 electrons shared. Then, you divided the shared electrons by 2 and you get the amount of chemical bonds. Then you need the formula. For this atom the formula would be H
/
H-C -H
/
H
Page 11: This is just a page of practice problems
Ex: H2O
Ans: There are 12 electrons needed, there are 8 electrons between H2 and O. There are 4 electrons shared. There are 2 bonds. Based upon this information, the formula would look like this ..
H-O-H
..
Page 12: Lewis Structures 2
Ex: Which elements are allowed to break the octet rule?
Ans: Elements allowed to break the octet rule if they do not have a full shell of valence electrons.
Ex #2: Does element A violate the octet rule?
/ / /
A
/ / /
Ans: Yes because each of those lines has two electrons in it and A would have more than eight electrons with those connected to it.
Page 13: More practice formula pages
Ex: What is the Lewis Structure for HCN?
Ans: There are 18 electrons needed, they have 10 electrons combined, therefore there are 8 electrons shared which means that there are 4 bonds. The formula would look like this:
H=C=N
Page 14: Lewis Structure 3
Ex: Draw the Lewis structures for carbon tetra-fluoride.
Ans: First you have to realize that that is CF4. Once you have done this, you can solve. Together they need 40 electrons. They have 20 electrons, this means that they share 20 electrons which comes out to 10 bonds. The formula would look like this:
.. ..
F F
/ /
C
/ /
F F
.. ..
Page 15: This is the final page of the journal and it is half of a page of practice problems.
Ex: Name the group of elements that X would belong to.
X .
Ans: X would belong to the Alkali metals group because it only has one valence electron and alkali metals only have one valence electron.
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