Video Transcript
Which of the following is not a
molecule? A) CO₂, B) O₂, C) NO, D) N₂, or E)
Na.
A molecule is two or more atoms
covalently bonded together. An example of this would be a molecule of
water, or H₂O, where we have one oxygen atom covalently bound to two hydrogen atoms. We can use the periodic table to work out
what the symbols in all our formulas mean.
If we look up the letter C on the
periodic table, we’ll see that it stands for the element carbon. So, when we look at our formulas, we can
see whenever we see a capital C like that, it indicates we’ve got one carbon atom. O is the symbol for oxygen. So, where we see O, we know we’re talking
about an oxygen atom. And when we see a little two, that means
we have two of that thing. So, O₂ means two oxygen atoms. This is the symbol for an oxygen
molecule, two oxygen atoms covalently bonded together. So, we know it’s not the correct answer
because we’re looking for something that’s not a molecule.
The last symbols are N for nitrogen and
Na for sodium. Elements’ symbols are always a capital
letter or a capital letter followed by a lowercase letter. So, the N in Na isn’t for nitrogen; it’s
just the beginning of Na for sodium. Now, the main difference between sodium
and nitrogen is that sodium is a metal and nitrogen is a nonmetal.
Now, we can still get nitrogen atoms and
sodium atoms, but nonmetals tend to form covalent bonds and form molecules, while metals
form metallic structures that continue in all directions and have very different bonding to
the covalent bonding in molecules. So, CO₂, O₂, NO, N₂ all describe a
molecule containing two or more atoms covalently bonded together. But Na describes a single atom. And it’s a single atom of a metal that
would be unlikely to form molecules in the first place. So, of our five candidates, the only one
that is not a molecule is Na.
