# 1.8 Electronic configurations of atoms

So up to this point, you know that an atom consists of energy levels called shells and these shells are divided into subshells in which electrons are located. The arrangement of electrons in the shells and sub-shells of an atom is called its electronic configuration.

This may sound a little obscure so far, but by looking at a few specific examples the picture becomes clearer.

Let’s go back to hydrogen once again.

How many electrons are found in the hydrogen atom?

### Answer

One

So the question is; into what sub-shell does this electron go?

The answer is pretty intuitive – it goes into the lowest available energy level.

The lowest energy shell is defined by the principal quantum number n = 1, and this contains an s sub-shell (only). So that’s where the single electron in hydrogen goes.

This is denoted 1s1, where 1 represents the main energy level (the shell) and s is the subshell. The superscript 1 represents the single electron occupying this energy level.

But what about more complicated atoms, i.e. those with greater atomic numbers than one? This is covered in the next section.

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