The electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbital . For example, the electron configuration of the neon atom is 1s2 2s2 2p6.

3. The electrons in the outermost occupied shell (or shells) determine the
chemical properties of the atom; it is called the valence shell. Each shell
consists of one or more sub shells, and each sub shell consists of one or
more atomic orbital's.
For example, hydrogen has one electron in the s-orbital of the first shell,
so its configuration is written 1s1. Lithium has two electrons in the 1s-
subshell and one in the (higher-energy) 2s-subshell, so its configuration is
written 1s2 2s1 (pronounced "one-s-two, two-s-one").
A sub shell is a subdivision of electron
shells separated by electron orbital.
Subs hells are labeled s, p, d, and f in an
electron configuration. Examples: The
first electron shell is the 1s subs hell.
The second shell of electrons contains
the 2s and 2p subs hells.