1.3 Ion

The atom as a whole is neutral，because the number of negative charges equals to that of positive charges. If an electrical imbalance is created in the atom by the removal or addition of one or more electrons，the result is an ion. Thus，an ion is an electrically charged atom （or molecule）. It can be either positive or negative，depending on whether it could contain fewer electrons or more electrons than the neutral atom （or molecule） does.^④ When an atom gains one or more electrons，it acquires a negative charge and is known as an anion; when an atom loses one or more electrons，it acquires a positive charge and is known as a cation. For example，the hydrogen ion，H⁺，is a cation and has one free proton，and the fluoride ion，F^-，contains an extra electron and is an anion.