The way in which electrons are arranged around a nucleus and the
effect that this has on chemical behavior are the subject of the
At the moment, notice only the trend from metals, to nonmetals,
to an inert gas, and the beginning of a repetition of properties
with the inert gas neon and the soft metal sodium.
Chemical properties are periodic functions of the atomic
number - in a listing of elements by increasing atomic number, similar
properties are encountered again and again at regular intervals.
This is one of the most important generalizations in chemistry.