CHEMISTRY HELP PLZ. THNX. dealing with identifiying compunds and finding wat is a central atom?

Question

i'm having trouble with this problem:
you are given a white crystalline powder that melts at 450 degrees celsius. you are told that the compound may either be NH4(subscript 4)Br or NO2(subscript2). what is the identity of the compound?

another problem i'm having is figuring out what a central atom is cuz i forgot(oops :) ) can you tell me wat a central atom of C2H4

thankx bunches :)

Answer 1

The first part of your question would be NH4Br due to the strong intermolecular forces giving it such a high melting point

In C2H4 the two carbons would both be considered the central atoms

it would be C(doublebond)C

and 2 hydrogens coming of each of them
From this you can determine geometries and also the hybridization of the parts of the molecule. Trigonal planar on each carbon, which gives it an sp^2 hybridization

Answer 2

It's hard to answer the question in the way that your teacher wants you to know it. NH4NO2 would go poof! long before it got to 450C. I looked up ammonium bromide in the Handbook of Chemistry & Physics, which says that it sublimes (changes directly from solid to vapor) at 452C.

Also, there is no central atom in ethylene ,C2H4. The structure is

H2C=CH2