Monday, January 14, 2008
CHEM CLASS WARNING!
I am unpleasantly surprised by some of you. I just went through the homework papers. Many of you did okay (two or three things to review before the test), some did great, but some (at least six) of you are clearly about to FAIL the next test if you do not sit down and study your notes and do practice problems by USING your notes. If you are taking the time to read this, you probably did not make the errors discussed below but, just in case...
Two MAJOR problems that I EXPLICITLY forewarned about:
As you must know by now (just from knowing the structure of table salt, sodium chloride i.e. NaCl), METALS CANNOT EVER COVALENTLY BOND TO NONMETALS. Do not EVER put a DASH between a METAL and a NONMETAL in ANY Lewis Structure. Dashes symbolize COVALENT BONDS. Nonmetals ALWAYS GAIN/STEAL electrons from metals (you know, Zeff!) so IONS MUST FORM and are arranged in a LATTICE. That is the case for EVERY metal-nonmetal compound. ALL Lewis Diagrams of IONS MUST BE IN BRACKETS!!!! THE CHARGE OF THE ION MUST BE WRITTEN, SIGN FIRST, THEN NUMBER, OUTSIDE OF THE BRACKET.
Look at your notes; copy your notes; get comfortable writing correct information. We did MANY examples of Lewis structures for salts/ionic compounds.
Secondly, when you write the formula for a salt, ANY SALT, like NaCl, do so just as you do for sodium chloride. That means, in your FINAL answer, do NOT EVER put + or - signs, charges etc. in the final formula. ALL salts are electrically balanced, like NaCl, which is why we do not write Na + + Cl - as the formula. Yes, those ions exist, but that is NOT how we have ever written any formula (see notes for proof).
For you own sake, DO NOT make those mistakes on Wednesday's test. DO come to extra help; clearly some of you need A LOT of it before Wednesday.
The formula of any salt SHOULD be figured out BEFORE you attempt to draw the Lewis Structures of the ions or else you will waste a LOT of time.
CLEARLY, too many of you are not looking at or using your notes when you do the homework. I read at least 10 papers with IDENTICAL completely wrong answers that do not remotely look like anything from our notes.
Two MAJOR problems that I EXPLICITLY forewarned about:
As you must know by now (just from knowing the structure of table salt, sodium chloride i.e. NaCl), METALS CANNOT EVER COVALENTLY BOND TO NONMETALS. Do not EVER put a DASH between a METAL and a NONMETAL in ANY Lewis Structure. Dashes symbolize COVALENT BONDS. Nonmetals ALWAYS GAIN/STEAL electrons from metals (you know, Zeff!) so IONS MUST FORM and are arranged in a LATTICE. That is the case for EVERY metal-nonmetal compound. ALL Lewis Diagrams of IONS MUST BE IN BRACKETS!!!! THE CHARGE OF THE ION MUST BE WRITTEN, SIGN FIRST, THEN NUMBER, OUTSIDE OF THE BRACKET.
Look at your notes; copy your notes; get comfortable writing correct information. We did MANY examples of Lewis structures for salts/ionic compounds.
Secondly, when you write the formula for a salt, ANY SALT, like NaCl, do so just as you do for sodium chloride. That means, in your FINAL answer, do NOT EVER put + or - signs, charges etc. in the final formula. ALL salts are electrically balanced, like NaCl, which is why we do not write Na + + Cl - as the formula. Yes, those ions exist, but that is NOT how we have ever written any formula (see notes for proof).
For you own sake, DO NOT make those mistakes on Wednesday's test. DO come to extra help; clearly some of you need A LOT of it before Wednesday.
The formula of any salt SHOULD be figured out BEFORE you attempt to draw the Lewis Structures of the ions or else you will waste a LOT of time.
CLEARLY, too many of you are not looking at or using your notes when you do the homework. I read at least 10 papers with IDENTICAL completely wrong answers that do not remotely look like anything from our notes.
# posted by C @ 1:51 PM 
