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Cations vs Anions

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Ions are charged species that are formed by the transfer of electrons from the outermost shell. Ions are either positive or negative in nature depending on the overall charge of the ion. If an atom loses an electron it has excess proton forming positive ions whereas if an atom gains an electron it has excess electrons forming negative ions.

In an aqueous solution of sodium chloride (NaCl), Na exists as a positive ion (cation) Na+, while Cl exists as a negative ion (anion) Cl. Because both of them have opposite charges they are attracted to one another creating an ionic bond.

Let’s learn more about ions, their types (cations and anions), and the difference between cations and anions in this article.

What is an Ion?

Ions are charged species that are formed when an atom loses or gains electrons. The word ion is derived from the Greek word ἰόν which means ‘going’. If an atom transfer electrons from its outermost orbit it tends to form an ion. Ions are formed in both cases when an atom loses an electron or when an atom gains an electron. Ions are formed by the atoms to attain the nearest noble gas configuration. As we know atoms are electrically neutral species, so

If an atom loses an electron the total positive charge exceeds the total negative charge and an overall positive charge is gained by the atom the atom, in this case, is called a cation. Some examples of cations are Na+, Ca+, Fe2+, etc.

Similarly, if an atom gains an electron the total negative charge exceeds the total positive charge, and an overall negative charge is gained by the atom, and the atom in this is called an anion. Some examples of anions are O2-, OH, Cl, etc.

The image below shows the formation of cations and anions.

Cations and Anions

 

On the basis of the number of elements in an ion, ions are classified into two categories,

  • Monoatomic Ions: Ions formed by only one atom are classified as monoatomic ions they can be either positive or negative. Example, Na+, Cl, etc.
  • Polyatomic Ions: Ions formed by a group of atoms are classified as polyatomic ions they can be either positive or negative. Example, (NH4)+, CN, etc.

What are Cations?

Cations are ions with a positive charge. When a metal loses its electrons, they form. They lose one or more electrons but none of their protons. As a result, they have a net positive charge. Calcium (Ca2+), potassium (K+), and hydrogen (H+) are examples of cations.

Formation of Cations

The most common cations of the typical elements are those in which all of the valence electrons have been lost. Consider sodium, an alkali metal. In the third major energy level, it has one valence electron. The sodium ion now has an octet of electrons from the second major energy level after losing that electron. An atom and an ion of a different atom (or two separate ions) that have the same electron configuration are referred to be isoelectronic. The sodium ion and the neon atom are isoelectronic.

Formation of Cations

 

Example of Cation: Sodium Ion

The ionization of the sodium atom produces a monoatomic monocation of the sodium atom. The sodium ion has a chemical formula of Na+ and an ionic radius of 0.102 nm. Sodium ions are required for a variety of physiological functions in the body, including the regulation of body fluids such as blood, nerve impulse transmission, heart activity, and other metabolic functions. The image given above shows the structure of Sodium cations.

Properties of Cations

Various properties of the cations are,

  • Cations are normally made up of metal atoms, however positive radical ions, such as ammonium ion (NH4+), can have several atoms.
  • Because they have more protons than electrons, cations are positively charged. As a result, cations have an electron deficit.
  • The ionic radius of cations is used to determine their size, and cations have a smaller radius than their parent atoms in general because they have one orbit less.
  • The smallest cation with no electron is hydrogen, which is substantially smaller than its parent atom.
  • In crystalline materials, anions take up the majority of the lattice space, leaving cations to fill in the gaps.
  • Cations are highly reactive in the gaseous state and will react with anions to generate neutral molecules. Cations, on the other hand, can exist in both liquid and solid states.
  • Cation interacts with the solvent in the liquid state to generate solvated ions, which are significantly more stable.

What are Anions?

Anions are ions with a negative charge. When a non-metal gains electrons, they form. They receive one or more electrons but keep all of their protons. They have a net negative charge as a result. Iodide (I), chlorine (Cl), and hydroxide (OH) are examples of anions.

Formation of Anions

Non-metal atoms frequently gain electrons until their outermost main energy level reaches an octet. except for neon, all of these anions are isoelectronic. The greatest number of electrons obtained in the production of anions is three-under ordinary conditions.

Formation of Anions

 

Example of Anion: Chloride Ion

The chloride ion is a monoatomic monoanionic ion produced when the chlorine atom is ionized. Chlorine is a non-metal that takes the shared pair of electrons after a bond breaking, resulting in a negative charge. The chlorine ion has a chemical formula of Cl and an ionic radius of 0.181 nm. The chloride ion is an electrolyte that is found in practically all bodily fluids. The image given above shows the structure of Chloride Ion

Properties of Anions

Various properties of the anions are,

  • Negative radical ions, such as the sulfate ion (SO4), are commonly produced from non-metals; nevertheless, negative radical ions can have several atoms.
  • Because anions contain more electrons than neutrons, they are negatively charged. As a result, anions have a lot of electrons.
  • Ions are measured by their ionic radius, and anions, in general, have a bigger radius because they contain more electrons repelling each other, resulting in a larger size than their parent atoms.
  • Because anions are larger than solids, they take up the majority of the space in the crystal.
  • Anions are highly reactive in the gaseous state and will react with cations to generate neutral molecules. Anions, on the other hand, can exist in both liquid and solid states.
  • An anion interacts with the solvent in the liquid state to generate solvated ions, which are significantly more stable. An anion interacts with the solvent in the liquid state to generate solvated ions, which are significantly more stable.

List of Cations and Anions

Various cations and anions which we observe regularly are discussed below in the  table

Table for Cations

Some important cations that are widely used are,

Chemical Name Chemical Symbol
Sodium Cation Na+
Calcium Cation Ca2+
Silver Cation Ag+
Aluminum Cation Al3+
Hydronium Ion H3O+
Ammonium Ion (NH4)+ 
Ferric Ion Fe3+
Cupric Ion Cu2+

Table for Anions

Some important anions that are widely used are,

Chemical Name Chemical Symbol
Chloride Anion Cl
Iodide Anion I
Oxide Anion O-2
Hydroxide Ion OH
Sulfate Ion (SO4)-2
Permagnate Ion (MnO4)
Dichromate Ion (Cr2O7)-2
Cyanide Ion CN

Difference Between Anions and Cations

Cations

Anions

A positive-charged ion or charged particle with a positive (+) charge on it, is referred to as a Cation.  An anion is a negatively charged ion or a charged particle with a negative (-) charge.
The number of protons in cations is greater than the number of electrons.  The number of electrons in anions is greater than the number of protons.
Metals, in general, produce cations.  Non–metals, in general, produce anions.
In electrolysis, cations are drawn to the negatively charged electrode.  In electrolysis, anions are drawn to the positively charged electrode.
Cations absorb electrons and become neutral atoms or molecules. Anions usually lose electrons and become neutral atoms or molecules.
Ionic compounds are formed when cations establish electrostatic or ionic connections with anions. Ionic compounds are formed when anions establish electrostatic or ionic connections with cations.
Cations are much smaller than anions. Anions are often bigger than cations.
e.g.  Na+, Mg+2, etc. e.g. Cl, Br, etc.

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FAQs on Cations and Anions

Q1: What are Cations?

Answer:

Positively charged ions are called Cations. They are formed when an atom (especially a metal) losses some electrons from its outermost shell. Some examples of cation are Sodium Cation (Na+), Calcium Cation (Ca2+), (H+), etc.

Q2: What are Anions?

Answer:

Negatively charged ions are called Anions. They are formed when an atom (especially a non-metal) gains some electrons in its outermost shell. Some examples of anions are Iodide Anions (I), Chloride Anion (Cl), Hydroxide Ion (OH), etc.

Q3: How are cations and anions formed?

Answer:

If an atom loses some electrons Cations are formed whereas if an atom gains some electrons Anions are formed.

Q4: How to identify cations and anions?

Answer:

If an ion is written with a positive charge it is considered to be a cation whereas if an atom is written with a negative charge it is considered an anion.

Q5: Why cations are smaller and anions larger?

Answer:

Cations are smaller than comparative anions because cations are formed by donating the electrons resulting in reducing their atomic radius whereas anions are formed by accepting the electrons resulting in expanding their atomic radius.

Q6: How to find cations and anions in compounds?

Answer:

To find cations and anions in a compound we simply dissolve the compound in water and it breaks the compound into its specific ions now the ion with a positive charge is called a cation and the ion with a negative charge is called an anion.

Q7: Why do Ions conduct Electricity?

Answer:

Ions conduct electricity because on dissolving in an aqueous solution they can easily conduct electric charges.

Q8: What is the use of cations and anions?

Answer:

Cations and Anions play a significant role in our lives. Sodium, Potassium, and Magnesium ions are required by our body for the control of blood pressure and the contraction of muscles. Calcium Ion is the key element in the making of the human bones.


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Last Updated : 03 May, 2023
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