If an atom, or atoms, has a balanced number of electrons (negative sầu charge) và protons (positive charge) they are neutral overall. However, if they are not balanced, they will be charged. These charged species are called ions.

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What is a cation?

A cation has more protons than electrons, consequently giving it a net positive sầu charge. For a cation khổng lồ size, one or more electrons must be lost, typically pulled away by atoms with a stronger affinity for them. The number of electrons lost, và so the charge of the ion, is indicated after the chemical symbol, e.g. silver (Ag) loses one electron lớn become Ag+, whilst zinc (Zn) loses two electrons khổng lồ become Zn2+.



What is an anion?

An anion has more electrons than protons, consequently giving it a net negative charge. For an anion to khung, one or more electrons must be gained, typically pulled away from other atoms with a weaker affinity for them. The number of electrons gained, and so the charge of the ion, is indicated after the chemical symbol, e.g. chlorine (Cl) gains one electron to lớn become Cl-, whilst oxygen (O) gains two electrons khổng lồ become O2-.


Cation vs anion chart

The main differences between cations & anions are summarized in the table below.






Electrode attracted to

Cathode (negative)

Anode (positive)

Formed by

Metal atoms

Non-metal atoms


Sodium (Na+), Iron (Fe2+), Ammonium (NH4+)

Chloride (Cl-), Bromide (Br-), Sulfate (SO42-)

Metallic atoms hold some of their electrons relatively loosely. Consequently, they tover to lớn thua kém electrons and form cations. Conversely, most nonmetallic atoms attract electrons more strongly than metallic atoms, và so gain electrons khổng lồ khung anions. Therefore, when atoms from a metallic & a nonmetallic element combine, the nonmetallic atoms tkết thúc khổng lồ draw one or more electrons away from the metallic atoms lớn khung ions. These oppositely charged ions then attract one other khổng lồ khung ionic bonds và produce ionic compounds with no overall net charge. Examples include calcium chloride (CaCl2), potassium iodide (KI) và magnesium oxide (MgO).

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Cation vs anion periodic table

It can be possible to predict whether an atom will size a cation or an anion based on its position on the periodic table. Halogens always khung anions, alkali metals and alkaline earth metals always khung cations. Most other metals form cations (e.g. iron, silver, nickel), whilst most other nonmetals typically size anions (e.g. oxygene, carbon, sulfur). However, some elements are capable of forming both cations và anions given the right conditions. One example is hydroren, which may gain (H-) or thua thảm (H+) an electron, forming hydride compounds such as ZnH2 (where it is an anion) và hydron compounds such as H2O (where it is a cation).

Elements in group 18 of the periodic table – the “noble gases”, tkết thúc not to lớn size ions due to lớn the arrangement of their electrons which makes them generally unreactive sầu.


Cation vs anion size

Cations và anions come in many sizes across the periodic table, as seen in this video clip.

Utilizing ionic properties

Ionic properties can be exploited by chemists for a range of purposes. Ion-exchange chromatography for example relies on the affinity of the molecules being separated for the stationary phase based on their charge properties to lớn enable separation.

Ionic properties are central to the function of batteries too. Batteries have two electrodes made of conductive sầu material, the cathode which is the positive sầu end where the electrical current leaves/electrons enter, and the anode where the electrical current enters/ electrons leave. In between the electrodes is an electrolyte liquid or gel that contains charged particles – ions. As this ionic substance reacts with the electrodes it generates electrical current. In single use, dry cell batteries, zinc is commonly used as the anode whilst manganese dioxide is a popular choice for the electrolyte cathode. The zinc anode also acts as the battery’s container in zinc-carbon batteries so as it oxidizes during use, the contents can start to leak over time.