What is a cation example?

An anion, pronounced [ an-ahy-uhn ], is a type of ion—an electrically charged atom or group of atoms. A cation is a type of ion for cats (OK, fine, that’s not true, but it is pronounced [ kat-ahy-uhn ] ). But seriously: anions and cations are both ions. The difference is in the electrical charge. Anions have a negative charge, and cations have a positive charge.

Before we talk about what exactly that means (and why it matters), let’s talk about what we mean by charge. Electric charge is a basic property of elementary particles of matter (protons, electrons, and neutrons). The protons in an atom have a positive charge, the electrons have a negative charge, and the neutrons have zero charge.

In an ordinary atom, the number of protons equals the number of electrons, so the atom normally has no electric charge one way or the other. An atom becomes negatively charged if it gains extra electrons, and it becomes positively charged if it loses electrons. We use the word ion to refer to atoms that have a charge one way or another, and we use the words cation and anion to specify whether the charge is positive or negative.

⚡️ Quick summary

Cations are positively-charged ions (atoms or groups of atoms that have more protons than electrons due to having lost one or more electrons). Anions are negatively-charged ions (meaning they have more electrons than protons due to having gained one or more electrons). Cations are also called positive ions, and anions are also called negative ions.

What is a cation?

A cation is an ion with positive charge, which means it has more protons (positively-charged particles) than electrons (negatively-charged particles). Cations are formed when an atom loses one or more electrons: the loss of the negatively-charged electron(s) results in an overall positive charge.

What is an anion?

An anion is an ion with negative charge, meaning it has more electrons than protons. Anions are formed when an atom gains one or more electrons: the gain of the negatively-charged electron(s) results in an overall negative charge.

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What is the difference between cations and anions?

The difference between cations and anions is, of course, their charge. But this difference in charge has an impact on how cations and anions behave and react.

One example is in the process of electrolysis, which involves an electric current passing through a material and producing a chemical reaction. During electrolysis, the positively charged cations are attracted to a negatively-charged electrode called a cathode. Anions are attracted to a positively-charged electrode called an anode.

In chemistry, cations are indicated with a plus sign (+) and anions are indicated with a minus sign (-), with the number of symbols indicating the number of electrons lost or gained (this is called an atom’s valence). For example, the symbols Na+ and Ca++ indicate cations, while Cl- indicates an anion.

Where do the words cation and anion come from?

The first records of the words cation and anion in English come from around the 1830s. Cation comes from the Greek katión, meaning “going down,” and anion comes from the Greek aniṓn, “going up.” The cat- in cation is a form of cata-, meaning “down” (it’s the same root used in cathode and catalyst). The an- in anion is a form of ana-, meaning “up” (it’s the same root used in anode). The word ion comes from the Greek ión, meaning “going,” and was introduced by English physicist and chemist Michael Faraday in the 1830s.

Remember: the number of electrons in a cation has gone down, resulting in a positive charge. The number of electrons in an anion has gone up, resulting in a negative charge.

Is oxygen a cation or an anion?

Many elements can take the form of either anions or cations depending on the situation. Oxygen often exists in a neutral state, but oxygen atoms tend to form anions by gaining two electrons. Atoms of other elements also tend to form anions, including nitrogen, chlorine, and fluorine, among others. By contrast, atoms of calcium, magnesium, aluminum, and sodium tend to lose electrons and form cations. Sodium chloride—what we know as table salt—is actually composed of an anion and a cation (written as NA+CL-).

How to use cation vs. anion

Remember, cations are positive ions—they are positively charged because they have lost one or more electrons and therefore have more protons than electrons.

Anions are negative ions—they are negatively charged because they have gained one or more electrons and therefore have more electrons than protons.

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

Cations are ions that are positively charged. Anions are ions that are negatively charged. Ions are charged atoms or molecules. If a balanced atom loses one or more electrons, it will become a positively charged cation. If a balanced atom gains one or more electrons, it will become a negatively charged anion. 

What is a cation?

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

What is an anion?

An anion has more electrons than protons, consequently giving it a net negative charge.

For an anion to form, 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 become Cl-, whilst oxygen (O) gains two electrons to become O2-.

Cation vs anion chart

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

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

Cation vs anion periodic table

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

Elements in group 18 of the periodic table – the “noble gases”, tend not to form ions due to the arrangement of their electrons which makes them generally unreactive.

Cation vs anion size

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

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 enable separation.

Ionic properties are central to the function of batteries too. Batteries have two electrodes made of conductive material, the cathode which is the positive 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.

A zinc-carbon dry cell battery (left) and alkaline battery (right).

In rechargeable batteries, such as many lithium-ion batteries, this chemical process is reversible and the internal structure different which allows the batteries to be recharged.

Due to the ionic properties of salt water, scientists are now striving to exploit the ionic electricity-generating potential of salinity gradients where salt water and fresh water mix as a green source of energy generation for the future.