11.09.2010

ANNOUNCEMENTS: 1. There will be a total of 6 quizzes, one everyday 2. If you're absent before a quiz, that quiz will be the one that's dropped 3.You can drop one quiz and retake one quiz 4. We taped in pages 9 to 15

HOMEWORK: Finish pages 11 to 13

Today in class we learned how to make Lewis dot structures for formulas like CH4 or F2 and others like the examples below:

Before drawing the actual structure, Mr. Paek suggests doing N, H, S and B every time because it makes it a lot easier. These letters stand for Need, Have, Share and Bonds. 

• NEED: you put the number of electrons needed to be stable, for most elements it's 8, but for Hydrogen it's 2. Then add all of it together.
• HAVE: the number of valence electrons then add it all up. 
• SHARE: subtract the number of valence electrons from the sum of the electrons needed. 
• BONDS: you divide the number shared by 2.

For example: The formula SeF2

• N= 24 (Se needs 8 electrons and F2 needs 2 sets of 8 because of the subscript "2", so you do 8+8+8=24)
• H= 20 (Se has 6 valence electrons and F2 has 7 and 7 because of the subscript "2", then you do 6+7+7=20)
• S= 4 (N-H or 24-20=4)
• B= 2 (4 divided by 2)

Once you're done with all that, you have to draw the structure.Using the same formula SeF2, Se would be in the center with two F's on either side, it doesn't really matter what side it's on as long as there are two F's. The bonds represent the lines from Se to the F's. Each line representing the number of electrons shared, which in this case is four, so two lines represent four electrons shared. The picture also has to have 20 total electrons in it because of the have. Since the lines already represent 4 electrons, you need 16 more, so you draw dots around the Se and the F's. I know this may sound confusing, but the picture below should make it easier to understand. The formula I used for this example is the first one below:

NEXT SCRIBER: Seena K.