Ions: Definition, Types & Examples

Any chemical species that holds a positive or negative charge of any magnitude can be defined as an ion. Often atoms and molecules with non-zero net charge are referred to as ions. In this article, we will explore this process of elements donating and accepting electrons and the type of charge they gain on themselves.

What are Ions?

The term ions can be defined as an atom or molecule which is charged. This charge can either be negative or positive.

Protons and neutrons are located in the centre of the nucleus and cannot be moved out of the atom whereas, electrons revolve around the nucleus in a fixed orbit and can either be taken out of an atom or added to an atom. This is done to attain a noble gas configuration by elements.

The charge is attained on the element due to an imbalance in the number of electrons and protons. Cations and anions are the two forms of ions.

History and Discovery of Ions

The word ion came from the Greek word which translates as “to go” and was introduced by English physicist and chemist Michael Faraday in \(1834\) for the then-unknown species that go from one electrode to another through an aqueous medium.

Although Faraday did not know about these species, he knew that since metals dissolved into and entered a solution at one electrode, some substance has moved through the solution in a current.

Cations

These are the ions that have a positive charge on them. This happens when electrons are donated, and the number of protons becomes greater than that of electrons. Thus, a cation is generated when an atom loses one or more electrons. As a result, cations have fewer electrons than protons. For example, the ions of all the metal atoms are cations. Cations are usually denoted by a plus \(\left( + \right)\) sign at the superscript along with the number that denoted the number of electrons donated.

For example,

i. The sodium ion is denoted as \({\rm{N}}{{\rm{a}}^{\rm{ + }}}.\)

Sodium atom contains \(11\) protons and \(11\) electrons, and therefore, it has no overall charge, but when it donates its valence electron to attain the noble gas configuration, it gains a positive charge over its ion and becomes \({\rm{N}}{{\rm{a}}^{\rm{ + }}}.\)

ii. The magnesium ion is denoted as \({\rm{M}}{{\rm{g}}^{{\rm{2 + }}}}.\)

The magnesium atom has \(12\) electrons and \(12\) protons, and therefore, it has no overall charge, but when it donates its two valence electrons to attain a noble gas configuration, it gains two units of positive charges over its ion and becomes \({\rm{M}}{{\rm{g}}^{{\rm{2 + }}}}.\)

iii. The aluminium ion is denoted as \({\rm{A}}{{\rm{l}}^{{\rm{3 + }}}}.\)

The aluminium atom has \(13\) electrons and \(13\) protons, and therefore, it has no overall charge, but when it donates its three valence electrons to attain a noble gas configuration, it gains three units of positive charges over its ion and becomes \({\rm{A}}{{\rm{l}}^{{\rm{3 + }}}}.\)

Just like sodium, lithium atoms lose \(1\) electron and forms a lithium-ion \({\rm{L}}{{\rm{i}}^{\rm{ + }}}.\) However, it is not possible to remove more than three electrons from an atom due to the high energy required for this purpose.

Lithium-Ion Battery

Lithium-ion batteries are rechargeable batteries that are found in mobile phones, portable devices, and electric vehicles.

An anode, cathode, separator, electrolyte, and two current collectors (positive and negative) make up a battery. The lithium is stored in the anode and cathode. Through the separator, the electrolyte transports positively charged lithium ions from the anode to the cathode and vice versa. The mobility of lithium ions in the anode produces electrons, which build a charge at the positive current collector. The electrical current then passes from the current collector to the negative current collector via a powered device (cell phone, computer, etc.). The separator prevents electrons from flowingly inside the battery.

Anions

These are the ions that have a negative charge on them. This happens when electrons are accepted, and the number of electrons becomes greater than that of protons.

Thus, an anion is formed by accepting one or more electrons by an atom. Therefore, an anion contains more electrons than protons.

For example, the ions of all the non-metal atoms are anions except that of hydrogen and ammonium ion.

Anions are usually denoted by a negative \({\rm{( – )}}\) sign at the superscript along with the number that denoted the number of electrons accepted.

For example-

i. The chlorine ion is denoted as \({\rm{C}}{{\rm{l}}^ – }.\)

The chlorine atom has \(17\) electrons and \(17\) protons, and therefore, it has no overall charge, but when it accepts an electron to attain a noble gas configuration, it gains a negative charge over its ion and becomes \({\rm{C}}{{\rm{l}}^ – }.\)

ii. The oxide ion is denoted as \({{\rm{O}}^{{\rm{2 – }}}}.\)

The oxygen atom has \(8\) electrons and \(8\) protons, and therefore, it has no overall charge, but when it accepts two electrons to attain a noble gas configuration, it gains two units of negative charges over its ion and becomes \({{\rm{O}}^{{\rm{2 – }}}}.\)

iii. The nitride ion is denoted as \({{\rm{N}}^{{\rm{3 – }}}}.\)

The nitrogen atom has \(7\) electrons and \(7\) protons, and therefore, it has no overall charge, but when it accepts three electrons to attain a noble gas configuration, it gains three units of negative charges over its ion and becomes \({{\rm{N}}^{{\rm{3 – }}}}.\)

However, it is usually not achievable to add more than three electrons to an atom because of the great force of repulsion by the subsequent electrons from the anion.

Polyatomic Ions

Compound ions or polyatomic ions are ions that are created from groups of linked atoms and have either positive or negative charges.

For example, ammonium ion \({\rm{NH}}_4^ + ,\) is a compound ion is made up of two types of atoms joined together, nitrogen and hydrogen. Similarly, carbonate ion \({\rm{CO}}_3^{2 – },\) sulphate ion \({\rm{SO}}_4^{2 – },\) nitrate ion \({\rm{NO}}_3^ – ,\) and hydroxide ion \({\rm{O}}{{\rm{H}}^ – },\) etc.

Some of the polyatomic ions are given as follows-

Ionic Compounds

The compounds which are made up of ions are known as ionic compounds. In an ionic compound, the positively charged ions (cations) and negatively charged ions (anions) are held together by the strong electrostatic forces of attraction. The forces which hold the ions together in an ionic compound consist of an equal number of positive ions and negative ions, so the overall charge on an ionic compound is zero.

For example, sodium chloride is an ionic compound that is made up of an equal number of positively charged sodium ions \(\left( {{\rm{N}}{{\rm{a}}^{\rm{ + }}}} \right)\) and negatively charged chloride ions \(\left( {{\rm{C}}{{\rm{l}}^{\rm{ – }}}} \right).\)

The following are some of the most frequent ionic compounds, their formulae, and the ions that make them up.

The ionic compounds are made up of a metal and a non-metal except ammonium chloride, made of only non-metals.

Formula Unit of Ionic Compounds

An ionic compound is made up of a large number of positively and negatively charged ions that have been bonded together.

Sodium chloride is an example of ionic compound that consists of a large number of sodium ions \(\left( {{\rm{N}}{{\rm{a}}^{\rm{ + }}}} \right)\) and chloride ions \(\left( {{\rm{C}}{{\rm{l}}^{\rm{ – }}}} \right),\) so the actual formation of the sodium chloride compound should be \({\left( {{\rm{N}}{{\rm{a}}^{\rm{ + }}}{\rm{C}}{{\rm{l}}^{\rm{ – }}}} \right)_{\rm{n}}},\) where n is a very large number.

Thus, \({{\rm{NaCl}}}\) is the simplest formula of sodium chloride and not its actual formula.

A ‘formula unit’ of an ionic compound is the simplest combination of ions that generates an electrically neutral unit. It can be thought of as the smallest unit of the compound, and it is the equivalent of a ‘molecule’ of the compound.
\({\left( {{\rm{N}}{{\rm{H}}_4}} \right)_2}{\rm{S}}{{\rm{O}}_4}\) is the formula unit of ammonium sulphate, and it consists of two \({\rm{NH}}_4^ + \) ions and one \({\rm{SO}}_4^{2 – }\) ion.

Formula Mass

The term formula mass for ionic compounds is used in which individual atoms do not exist because ionic compounds do not consist of molecules. Therefore, using the term molecular mass is not appropriate for them.

An ionic compound’s formula mass is the molecular mass of its ‘formula unit’ as compared with the mass of carbon- \(12\) atom atoms.

Let us see an example to understand the concept of formula mass more clearly.

Solved Example on Formula Mass

Calculate the formula mass of potassium carbonate \(\left( {{{\rm{K}}_2}{\rm{C}}{{\rm{O}}_3}} \right)\)

Sol- Formula mass = Mass of \({\rm{2\,K}}\) atoms \(+\) Mass of one \({\rm{C}}\) atom \(+\) Mass of \({\rm{3O}}\) atoms of \({{\rm{K}}_2}{\rm{C}}{{\rm{O}}_3} = 2 \times 39 + 12 + 3 \times 16\).
\( = 78 + 12 + 48\)
\(= 138\,{\rm{u}}\)
Thus, \(138\,{\rm{u}}\) is the formula mass of potassium carbonate.

Summary

In this article, we studied in detail how charges are occupied on an atom on losing or accepting electrons. Now we know that the charge occupied is due to the imbalance of the number of protons. We also studied about the different types of ions- cations, anions, and polyatomic ions, and that an ionic compound is bonded by an electrovalent bond.

FAQs on Ions

Frequently asked questions related to ions is listed as follows:

Q.1. How are ions formed?
Ans: Ions are formed either by accepting electrons or donating electrons from a neutral atom. When the atom accepts an electron, the ion becomes negatively charged and is called an anion. When an electron is donated, the ion becomes positively charged and is called a cation.

Q.2. What are polyatomic ions? Give examples.
Ans: Compound ions or polyatomic ions are ions that are created from groups of linked atoms and have either positive or negative charges.
For example, ammonium ion \({\rm{NH}}_4^ +,\) is a compound ion is made up of two types of atoms joined together, nitrogen and hydrogen. Similarly, carbonate ion \({\rm{CO}}_3^{2 – },\) sulphate ion \({\rm{SO}}_4^{2 – },\) nitrate ion \({\rm{NO}}_3^ – ,\) and hydroxide ion \({\rm{O}}{{\rm{H}}^ – },\) etc.

Q.3. What is a hydronium ion?
Ans: The hydronium ion or hydronium is the name of the cation \({{\rm{H}}_3}{{\rm{O}}^ + }.\) It is produced when an Arrhenius acid dissolves in water.

Q.4. How does a lithium-ion battery work?
Ans: An anode, cathode, separator, electrolyte, and two current collectors (positive and negative) make up a battery. The lithium is stored in the anode and cathode. Through the separator, the electrolyte transports positively charged lithium ions from the anode to the cathode and vice versa. The mobility of lithium ions in the anode produces electrons, which build a charge at the positive current collector. The electrical current then passes from the current collector to the negative current collector via a powered device (cell phone, computer, etc.). The separator prevents electrons from flowingly inside the battery.

We hope this detailed article on the Ions will be helpful to you. If you have any questions regarding the article or in, general, about the ions, please ping us through the comments section, and we will get back to you as soon as possible.