A cation is a positively charged ion, formed when an atom (usually a metal) loses one or more electrons, for example Na+ or Mg2+.
A cation is a positively charged ion, formed when an atom loses one or more electrons. The atom is usually a metal. Malay: kation · Chinese: 阳离子.
When an atom loses electrons, it still has the same number of protons but fewer electrons, so the positive charge of the protons is no longer fully cancelled and the particle carries a net positive charge. This positive ion is a cation. Metals form cations easily because they have only a few outer electrons, which they lose to reach the stable arrangement of the nearest noble gas. The size of the positive charge equals the number of electrons lost, so a Group 1 metal forms a 1+ cation, a Group 2 metal a 2+ cation, and a Group 13 metal a 3+ cation.
Example. A sodium atom (2.8.1) loses one electron to become the cation Na+ (2.8). A magnesium atom (2.8.2) loses two electrons to become Mg2+ (2.8). The ammonium ion NH4+ is a polyatomic cation. In an ionic bond, it is the cation that is attracted to the anion.
Confusion to avoid. Do not mix up a cation with an anion. A cation is positive and is usually formed by a metal losing electrons; an anion is negative and is usually formed by a non-metal gaining electrons. A useful memory aid is that the “t” in cation can be read as a plus sign, and that a cation is attracted to the negative cathode in electrolysis.
The cation is one half of every ionic compound in this chapter, and identifying it and its charge correctly is the first step to writing a correct ionic formula in SPM Chemistry.
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