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Ion Definition – Types, Formation & Applications

Aug 12, 2022

What Are Ions?

Ions are chemically charged species that contain either a positive or a negatively charged quantity. It is an atom, group of atoms, or any subatomic particle with a net electric charge. An ion with a total positive charge is termed a proton, while an ion with a net negative charge is termed an electron.

A proton is also known as a cation, whereas you can call an electron an anion. The atoms that tend to form cations are generally known as metals, while those that tend to form anions are called non-metals. As a universally acknowledged fact, ions of opposite charges always attract each other.


In simple words, an ion or ions definition can be described as an electrically charged atom or group of atoms.

Ions Definition

An ion is formed by an atom’s loss or gain of electrons. Therefore, it contains an unequal number of electrons and protons. Some common examples of the ions are:


sodium ion (Na⁺), magnesium ion (Mg²⁺), chloride ion (Cl⁻), and oxide ion (O²⁻).

If an ion is formed by only one variety of atoms (each holding some gross charge, either positive or negative), in that case, the group of atoms can be referred to as a monatomic ion or an atomic ion. If two or more different atoms form an ion, they are called molecular or polyatomic ions.


History of Ions

The word ion is acquired from the Greek work ἰόν, which means ‘to go.’ Therefore, the term ‘ion’ implies ‘a goer.’ In 1830, ions were first introduced by Micheal Faraday. He described ions as electrically charged atoms or a family of atoms traveling toward a cathode or anode.

Later, in 1884, Svante August Arrhenius further proposed the mechanism of ions in his experiment. In 1903, he won the Nobel Prize for it.


Representing the Charge on an Ion

It is necessary to write the chemical formula of an atom before representing it in a charged ion form. Now, the magnitude of the charge on an ion is written in the superscript format next to the chemical formula of the ion.

After writing magnitude, move to the charge or sign of the magnitude, i.e., positive (+) or negative (-). If the magnitude is greater than -1, the charge of magnitude is written after the magnitude. For instance, the oxide ion is represented as O²⁻.


If the magnitude of the charge has a value equal to one (either + or -), you can omit the magnitude of the charge. For instance, as the charge on sodium ion is +1, you can write it as Na⁺.

Types of Ions

There are two kinds of ions: cations and anions.


1. A Cation or Positively Charged Ion:

Cations are called cations if an ion contains a positive charge with some magnitude, such as copper ion, Cu²⁺, etc. A cation is devised by the loss of one or more electrons by an atom. For instance, a sodium atom drops one electron to form a sodium ion, Na⁺, which is a cation.

As the cation is formed by removing one or more electrons from an atom, it means a cation has less number of electrons compared to its atom. In other words, a cation contains fewer electrons than protons.


2. An Anion or a Negatively Charged Ion:

Fluoride ions, F⁻, or sulfide ions, S²⁻, are called anions because they are negatively charged ions. An anion is devised by an atom’s gain of one or more electrons. For instance, a chlorine atom gains one electron to form a chloride ion, Cl⁻, which is an anion.

Since an anion is devised by adding one or more electrons to an atom, it means an anion has more electrons compared to a normal atom. In other words, an anion contains more electrons than protons.

How are Ions Created?

There are some ways to form ions in an atom. Some of them are

1. Physical Ionization Method:

When molecules of liquid or gaseous fluids collide spontaneously, electrons drop out from one of the atoms or molecules. As a result, cations and anions are formed. The free electron may connect to another molecule or atom, forming a new negatively charged anion.

2. Chemical Interaction Method:

When an ionic compound, like salt, is dissolved in an appropriate solvent, water, etc., the salt atoms dissociate, forming Na⁺ (sodium ion) and Cl⁻ (chloride ion) free ions.

3. Electrolytic Method:

This method passes electricity through certain conducting solutions, forming ions in the solution. After that, these ions are deposited on the cathode and anode.

Formation of Ions


If an element has 1, 3, or 2 electrons in its outermost shell, in that case, it tends to lose them to attain the stable configuration or octet. The loss of electrons is termed as formation of cations. Usually, metals have 3, 1, or 2 electrons in their valence shells. Therefore, the metals lose electrons to attain positively charged ions or cations.

For the sample, potassium, sodium, calcium, magnesium, aluminum, etc., are all metals that can donate their valence electrons to attain a cation state.


If an element has 5, 6, or 7 electrons in its outermost shell, in that case, it tends to gain them to attain the stable configuration or octet. The gain of electrons is termed as formation of anions. Usually, non-metals have 5, 6, or 7 electrons in their valence shells. Therefore, the non-metals gain electrons to attain negatively charged ions or cations.

For the sample, chlorine, fluorine, iodine, bromine, sulfur, oxygen, nitrogen, etc., are all non-metals that can accept electrons in their valence shells to attain an anion state.

Ions in Nature

  • Ions are widely spread in the natural world. They are transporters of electric current and are strongly affected by magnetic fields.
  • A body of ionized matter is called plasma. It behaves adversely from a solid, liquid, or gas.
  • There are various ionic compounds present on Earth. When these compounds dissolve in water, their cations and anions become isolated and are surrounded by water molecules.
  • Phosphate and calcium ions are indicated in the genesis of teeth and bones in the body.
  • Plants require magnesium, calcium, potassium, phosphate, and nitrate for proper development.

Applications of Ions

The properties of ions have caused many research, domestic, and industrial applications. Some examples are given below.

  • In electrolysis, the current is passed through the solution that contains ions.
  • Many smoke detectors contain an ionization chamber to interrupt the current flow and set off the alarm.
  • The ion exchange phenomenon is used to purify water.
  • Chemists and biochemists use ion exchange chromatography methods to separate pigments, the mixture of proteins, and other chemicals that carry electrical charges.
  • An ion engine or thruster is used in one mode of spacecraft propulsion.


An ion can exist in the form of a monatomic, polyatomic, or molecular ion. A monatomic ion that consists of a single atom is called a monatomic ion. In contrast, an ion that comprises more than one atom is called a polyatomic ion. Larger ions comprising many atoms are called molecular ions.

A positively charged ion is termed a cation. At the same time, negatively charged ions are called anions. Ions have different properties than normal atoms. They have several applications in different fields.

Frequently Asked Questions

1. Is there a change in the atomic number of the atoms when they convert into ions?

There is no change in atomic number in the formation of ions. The atomic number of an atom is identical to the protons’ number in its nucleus. Only the number of electrons gets changed when an atom forms its ion. At the same time, the protons’ number in the nucleus remains the same. Hence, there is no change in the atomic number of an atom in the formation of its ion.

2. Is there any change to the size of an atom in the formation of its ion?

Yes. The formation of an ion from its atom affects its size. The size of the cation is usually smaller than its atom’s size. At the same time, the size of an anion is normally greater than its atom’s size. The reason is the removal of an electron when forming a cation; the number of valence shells decreases. Whereas, during the formation of an anion, one or more extra electrons are added to the outermost shell of the ion. It results in the repulsion between electrons, so the size increases.

3. What are the differences between the properties of an atom and its ion?

The properties of an atom and its ion are completely different from each other. Some differences are:

  • Atom is an electrically neutral species, while its ion is a charged species.
  • An atom has an equivalent number of protons and electrons. In contrast, its ion has a different number of electrons and protons.
  • Due to the extra unstable outermost shell, an atom is a reactive species. In contrast, its ion attains inert gas electronic configuration and makes it stable.
  • There is also a difference between the atomic and ionic sizes, i.e., the cation is smaller than an atom, but the anion is greater than an atom.
  • The chemical properties of ions are also different from their atoms.
Ion Definition


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