Explanation:
When an atom tends to gain an electron then it forms a negatively charged ion. Whereas when an atom tends to lose an electron then it acquires a positive charge.
For example, any element having more than eight electrons in its valence shell will tend to lose electron(s).
And, any element having less than eight electrons will tend to gain electron(s).
Thus, we can conclude that in general, an atom with more than eight electrons in its valence shell tends to lose electrons and form a positively charged ion. An atom with less than eight electrons in its valence shell tends to gain electrons and form a negatively charged ion.
