Part of Asimov's essay collection, this essay is the most accessible introduction to the standard model of atom. It was published on November 1980.
All the countless myriads of things, living and non-living, large and small, here and in the farthest galaxies, can't really be countless myriads. That would be too complex, too messy to suit our intuition which is that the Universe is basically simple, and that all we need is to be subtle enough to penetrate that simplicity.
The Greeks suggested the Universe was made up of a few "elements,*' and some supposed that each element was made up of invisibly small "atoms” (from a Greek word meaning "indivisible”) which, as the name implied, could not be divided into anything smaller.
Nineteenth-century chemists agreed in essence. But what nineteenth-century chemists found were elements by the dozens, each with its characteristic atoms. Again, too complex and too messy.