What is a cation?

A cation is specifically defined as an atom or molecule that has lost one or more electrons, resulting in a net positive charge. The loss of electrons outweighs the number of protons, leading to this positive charge. This is crucial in various chemical reactions, especially in ionic bonds, where cations play a significant role in forming compounds with anions, which are negatively charged ions.

When considering the other choices, the definition highlights that a cation cannot be an atom that has gained electrons, as that would create an anion, which is negatively charged. Cations and anions are fundamental concepts in understanding chemical bonding and reactions. Additionally, while the concept of hydration is important in the study of molecules in solutions, a cation itself does not relate to the presence of water; thus, the option regarding a molecule that contains water does not fit the definition of a cation. The defining characteristic is the positivity due to electron loss, making it clear that the concept covered by the definition aligns with the understanding of positive ions in chemistry.