Re: Chapter 11 - Q&A - Q6
by goldstanda3269 » Wed Mar 01, 2017 5:32 pm
[quote="mehxsquare6375"]Hello, I am confused over the idea of formal charge...I thought I got it but I keep getting it wrong /: --------------------------------------6) Which of the following structures have a central atom with a formal charge of -1?[img]http://www.oatbooks.com/images/index_c93.png[/img]A. AB. B <<<<< answerC. CD. DE. EExplanation: On the Surface: With experience with your review and completing problems, hopefully you recognize that when nitrogen is bonded 4 times (ammonium), it has a positive charge; when it is bonded 3 times (i.e. ammonia), it is neutral; thus when it is bonded 2 times, it has a negative charge. [color=#FF00BF](I guess it is good to remember it like this but I hope to understand the concept too...)[/color]Going Deeper: The number of lone and bonding pairs of electrons on nitrogen will be 4. [color=#FF00BF](I dont understand why it is 4)[/color]The normal valency of the nitrogen atom is 3 [color=#FF00BF](I thought Nitrogen has 5 valence electrons...)[/color] and this can then be used be determined whether the charge is therefore positive (four bonds, E), negative (two bonds,B) or zero (three bonds, A, C and D). (This of course assumes that the total number of electrons around the nitrogen atom is 8, the balance made up with lone pairs which may or may not be explicitly indicated; CHM 3.5).-----------------------Please teach me how to get the answer ~Looking forward to the guidance!P.S. [color=#BF80FF]I quite like the colours thing[/color]"The number of lone and bonding pairs of electrons on nitrogen will be 4."- I think you know this one: many atoms like nitrogen follow the octet rule and are thus surrounded by 8 individual electrons which is the same as saying "The number of lone and bonding pairs of electrons on nitrogen will be 4." Be careful because the real GAMSAT is filled with twists in the ways that common things are described."The normal valency of the nitrogen atom is 3 (I thought Nitrogen has 5 valence electrons...) "- To be honest, most science students do not know the difference between valence electrons and valency, but they can quickly recognise whether or not common atoms (i.e. C, H, O, N) are fully bonded or not. Nonetheless, ...Yes, nitrogen has five valence electrons (= five electrons in its outermost shell). As alluded to above, these electrons may bond covalently with the electrons in other atoms in order to fulfill the octet rule, which would give nitrogen the 8 valence electrons it wants.This is why we say that nitrogen has a valency of 3: N wants three more electrons in its outer shell. NH3, for instance, is the classic example (often repeated) of nitrogen bonding covalently with three hydrogens (which each have one valence electron) to give the nitrogen a full eight electron in its valence shell. N2 with a triple bond and a lone pair for each atom is another good example: https://dr282zn36sxxg.cloudfront.net/da ... ARD_TINY.1