Chemblog!

This extended weekend's assigned Regents exams are posted even though they are in your Orange Review Book. I will post my analysis of certain important questions. You will notice that my analysis contains as many ILLUSTRATIONS as words! That is no accident and should be remembered and applied to most of the questions on your Regents. This way, you (and the graders) will be able to SEE and follow what you are writing about. Naturally though, a drawing, just by itself, generally will not suffice for an answer so always describe and label what you draw out.
"IN TERMS OF": these three important words are found in MANY part B-2 and part C questions. They are EXTREMELY important and must be explicitly followed! When a question asks for an answer IN TERMS OF a particular word or phrase, LOOK AT YOUR ANSWER and ask yourself, " Did I use the EXACT word or phrase that was asked for AND did I RELATE/show the relationship between the word or phrase and what was asked for"? For example, "in terms of electronegativity, explain why the C-O bond is polar" means that you must DEFINE the term "electronegativity", which is a measure of the degree of attraction of an element's nucleus for the electrons that are SHARED in a (covalent) BOND. Then you reason that, the HIGHER the electronegativity of an element, the GREATER its degree of attraction for shared electrons in a bond. Since, according to the Reference Tables, C has an electronegativity of 2.6 and O has an electronegativity of 3.5 AND the cutoff for considering a bond to be POLAR is an electronegativity DIFFERENCE of greater than 0.5, the C-O bond is polar because the difference in electronegativity is (3.5 - 2.6) 0.9. SO, Oxygen has a much greater attraction for the electrons shared in its covalent bond with Carbon, thus, the polar bond.
More test tips to come in class and on this blog...