A charged particle that forms when an atom transfers electrons is called an ion.

Here's why:

* Atoms are neutral, meaning they have an equal number of protons (positive charge) and electrons (negative charge).

* Ions are formed when an atom gains or loses electrons.

* Cations are positively charged ions formed when an atom *loses* electrons.

* Anions are negatively charged ions formed when an atom *gains* electrons.

Let me know if you'd like more details about ions or the process of ionization!