Final answer:
An atom becomes a negatively charged anion when it gains an electron, not a positive ion. Chlorine, for example, becomes Cl- when it gains an electron. If it loses an electron, it would become a cation, signifying a positive charge.
Step-by-step explanation:
When an atom gains an electron, it does not become a positive ion; instead, it becomes a negatively charged ion, also known as an anion. This is due to the increase in the number of negatively charged electrons compared to the positively charged protons within the nucleus. The resulting imbalance in charge creates a negative ion. For example, when a chlorine atom gains one electron, it becomes a chloride ion with a -1 charge.
Conversely, when an atom loses one or more electrons, it becomes a positively charged ion, or a cation. This occurs because there are fewer electrons to balance the charge of the protons. For instance, sodium losing one electron results in a Na+ cation.
To summarize, the rule is: atom gains electrons = anion (negative charge), atom loses electrons = cation (positive charge).