What is the symbol for a calcium ion?

The symbol for a calcium ion is represented as Ca(2+), indicating that it has lost two electrons and thus carries a positive charge of two. In the context of calcium, this occurs because calcium, which is located in Group 2 of the periodic table, typically loses two electrons in its outer shell to achieve a stable electron configuration similar to that of the nearest noble gas, argon. This electron loss results in the formation of a divalent cation, which is essential for various chemical reactions and the formation of compounds, such as calcium chloride or calcium carbonate.

Other options incorrectly depict the charge or valency of the calcium ion. For instance, Ca+ suggests a single positive charge, which does not reflect calcium's typical oxidation state. Similarly, Ca(2-) implies that calcium has gained two electrons, which is not the case for this element as it is a metal that primarily forms cations rather than anions. Ca2, while it denotes the element's atomic quantity, fails to represent any charge, which is critical for identifying ions in chemical contexts.