Answer 1:
There really is no limit to the size of
molecules.
Well, if you had a molecule the size of the
solar system, it would collapse under its own
gravity and form a black hole- but ignore
technicalities like that.
DNA strands are
single molecules, and they can be several inches
long, which is about a billion atom-lengths.
Despite their great length, these molecules aren't
much more than 10 atoms wide. DNA molecules pair
up and coil into chromosomes, which can be seen
with a good microscope.
Diamonds are also
single molecules, which is one reason for their
unusual hardness- to break a diamond, you must
break trillions of atomic bonds. The world's
biggest uncut diamond weighed 1 1/3 pounds, so
that molecule had 30 trillion trillion carbon
atoms! In diamond, each carbon atom connects to
four of its neighbors, forming a pyramid.
The
bonds form an interlocking network, like a 3-D
version of the triangular scaffolding you see on
bridges. Triangles have great structural strength,
which also contributes to the hardness of diamond.
Atoms are a bit like Zaks. You can build something
as big as you want, as long as you have enough
pieces and you follow the linking rules. Carbon
(C) and silicon (Si) must have four bonds,
nitrogen (N) and phosphorous (P) must have three,
oxygen (O) and sulphur (S) have two, hydrogen (H)
and chlorine (Cl) have one, etc.
There are
exceptions to these rules, but you can use them to
figure out how most molecules are put together.
Try it for simple molecules like water (H2O),
carbon dioxide (CO2), methane (CH4), nitrogen
(N2), cyanide (HCN), or hydrochloric acid (HCl).
If you're ambitious, try it for benzene (C6H6) or
alcohol (C2H5OH).
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