My favourite molecule is water.
I'd marry it, unless it was my daughter!
Its solid form floats on its liquid form,
which makes it far outside the norm.
It allowed life to form on ancient Mars,
and we use it to wash out cars.
H₂O! H₂O! H₂O!
Sorry but if you want fluffy balls you'll have to stick them on yourself (and in fact I urge you to do so...)
update: Embarrassingly the atomic (right?) mass was wrong. Fixed thanks to an awesome science teacher named Malia. If your science teacher is called Malia and she wears this shirt to class, you better be nice to her.