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.

Wednesday 9.1.10

Today, Mr. Paek started the class by talking about yesterdays scribe post. After going over what was good and what could’ve been changed, he let us go back to our chosen lab groups to finish up the measurement lab.

Most groups just had to measure the mass of four objects, and those objects were: a jumbo paperclip, a piece of paper, a pencil and an empty film canister. We used a balance pan to measure how much each object weighed in grams. Then, after measuring the mass, the last thing to do in the lab was to measure the temperature. We used a thermometer to measure the room temperature and the temperature of tap water in a beaker.

Once everyone finished the lab we regrouped and got four new sheets of paper to tape into our journal. Two of those sheets were about significant figures and the other two were about scientific notation.

The significant figures rules are:       

·         Digits other than zero are always significant

·         Zeros between non-zero digits are always significant

·         Any final zero use after a decimal point is significant

·         Zeros used solely for spacing the decimal point (place holders) are not significant

Examples are in the picture posted.

             Lastly, we ended the class by learning how to round numbers to four significant figures and how to convert measurements into scientific notation. To round numbers to four significant figures you take the first four significant figures and make the rest of the numbers after those zeros. For example 12,345,670 would become 12,350,000 or 0.0657030 would become .06570. Some people were really confused, but after doing a couple of examples we started to get it. Mr. Paek said that we will do some more examples in class tomorrow.