Which ion does an atom form?

The function arrangement is ready for you. You will write a function that finds the charge of the ion an atom forms from its outer electrons, count the electrons in that ion, and find the atoms whose ions have the arrangement of argon.

The idea. With $1$, $2$ or $3$ outer electrons, an atom loses them and its ion has that positive charge. With $5$, $6$ or $7$, it gains enough to make $8$ and its ion is negative. With $4$, or a full shell, it forms no simple ion.

Your tasks.

1. In ion_charge, return the charge: $+1$ to $+3$, $-1$ to $-3$, or $0$.
2. In ion_electrons, return the electrons in the ion: the atomic number minus the charge.
3. Find like_argon, the symbols in atoms whose ions have $18$ electrons.