How do you know if a Lewis Structure is an ion or not? And how do you figure out the charge?

Question

How do you know if a Lewis Structure is an ion or not? And how do you figure out the charge?

Answer 1

Count the electrons in the last shell of all the atoms. and compare it with the number they should have.

Answer 2

The Lewis structure of an ion should be enclosed in square brackets with the charge written as a superscript after the rightmost bracket, as in the following.  (Mentally insert the remaining lone pairs on the oxygen.)

[H-O:]^-