Anion vs Cation

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An ion is an atom or group of atoms in which the number of electrons is not equal to the number of protons, giving it a net positive or negative electrical charge. An anion is an ion that is negatively charged, and is attracted to the anode (positive electrode) in electrolysis. A cation has a net positive charge, and is attracted to the cathode (negative electrode) during electrolysis.

Comparison chart

Anion versus Cation comparison chart
	Anion	Cation
Definition	An anion is an atom or a molecule which is negatively charged, i.e. has more number of electrons than protons.	A cation is an atom or a molecule which is positively charged, i.e. has more number of protons than electrons.
Charge	Negative	Positive
Examples	(O2-), sulfide (S2-), fluoride (F-), chloride (Cl-), bromide (Br-), iodide (I-), nitride (N3-) and hydride (H-)	sodium (Na+), Iron (Fe2+), and Lead (Pb2+)
Etymology	The Greek word ano (up)	The Greek word kata (down)
Electrode attracted to during electrolysis	Anode	Cathode
Type of element	a nonmetal	a metal

Etymology

Anion originated from the Greek word ano, meaning ‘up’. The word cation originated from its Greek counterpart kata, which means ‘down’.

Mnemonic device

A good way to remember which type of ion is positively charged is to use the following mnemonic devices:

Anion: A Negative ION
CATion: PAWSitive (cats have paws)

Charge formation

When a cation like sodium is represented as (Na+), the ‘+’ charge that accompanies it, indicates that it has one less electron than the total number of protons. This uneven equation of electrons and protons enables sodium to have a positive charge. Similarly, when the chloride anion is represented with (Cl-), the ‘–‘charge indicates that it has one less proton than the total number of electrons. If the ‘+’ or the ‘-’ sign is accompanied by a number like +4 or -2, then it implies that: The cation with +4 charge has 4 less electrons than the total number of protons and The anion with -2 charge has two less protons than the total number of electrons.

Bonds

Sodium and chlorine bonding ionically to form sodium chloride.

As a result of being negatively and positively charged, anions and cations usually form bonds. These are known as ionic bonds and exist due to the mutual attraction of oppositely charged ions. They form a crystal bond, in which oppositely charged ions are bound to each other.