[seqfan] Re: Chemistry sequence

[William Keith]

Perhaps you could start from the simplest definition: covalence graphs 
for the outer electron shells.  Essentially, then, the sequence would 
count graph objects that can be described by Lewis dot structures, 
which have well-defined conventions.

H: A terminating vertex on the end of an edge
He: A singleton
Li, Be, B, C, N, O, F: vertices with 1, 2, 3, 4, 3, 2, or 1 edges, all 
distinct from the previous
Ne: A singleton distinct from He

Etc.

Many of the compounds thus described do not exist in nature (in any 
stable form, at any rate), of course, such as H-O-O-O-O-O-O-H, or Na-Cl 
(which is ionic rather than covalent), but as has been pointed out the 
more subtleties you include in that definition the more limited your 
class of compounds is going to be.

William Keith