The question appear to have been posted in Algebra whereas it belongs to Chemistry.
You already knew the answer when you said "I know that it has an atomic number of 9"
Atomic number of an element is the number of protons in the nucleus of that element. It is also the total positive charge, in the atomic nucleus.
It can be written as
The electronic configuration is
It tends to capture an electron easily to have the same electronic configuration of that of the noble gas neon.