Thursday
April 17, 2014

Homework Help: Chem

Posted by Anthony on Monday, March 12, 2007 at 12:05pm.

Draw a Structural Formulae for Hydrogen Cyanide (HCN) and Cyanogen (C2N2 or CN2)

Hydrogen = 1 Valency
Nitrogen = 3 Valencies
Carbon = 4 Valencies



H-C(triple bond)N
N(triple bond)C-C(triple bond)N

Thank you

And for a Lewis Structure

they would be H:C:::N:

and :N:::C:C:::N:

very good.

One thing i am confused with is stating the noble gas whose electron configuration is attained in the lewis structures?

HCN has 10

CN2 has 18

Would they simply be the Noble gases with the atomic numbers 10 and 18

Neon and Argon?????

From what I have answered for other students in the same class, I think there is some confusion over the noble gas configuration "for the molecule" vs the noble gas configuration "for the atoms." I have never heard of a noble gas configuration for the molecules but the noble gas configuration for the atoms is standard practice. In the latest two or three posts, students have posted this question as to the noble gas configuration for the atoms; therefore, assuming this is what you meant, the H now has the noble gas configuration of He, C and N have noble gas configurations of Ne. Each atom has attained the noble gas that is the next highest noble gas; i.e., for H it is He and for C and N it is Ne.

That is the way I would interpret it IF you are looking for the molecule; however, let me point out the difference.
For the atom, C has 6 electrons and the next noble gas is Ne with 10. N has 7 electrons and the next noble gas is Ne with 10. HCN has 10 electrons (but these ten electrons are in the outer shell only.--What about the other 2 electrons in C and the other 2 electrons in N that are not shown in molecular drawings?). When we talk about atoms being isoelectronic with the next higher noble gas we are talking about the total number of electrons and not just those in the outside shells. You must decide which it is. Read the question carefully. Apparently some students are reading it as the molecule and others are reading it as the atoms.

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