To discuss, we must revise our concepts about atoms. Let’s get a quick review of the subatomic particles present in the atom.
Firstly, the atom is defined as the smallest unit of matter and has subatomic particles as mentioned below:
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Protons: They are positively charged particles.
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Neutrons: They are neutral particles.
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Electrons: They are negatively charged particles present in the orbits outside the nucleus.
When the number of protons is equal to the number of electrons it is considered a neutral atom. This means that to balance every negative charge there is a positive charge for it. But in some cases, the number of electrons may exceed the number of protons or vice-versa which creates an imbalance within the atom’s charge and thus forms an ion.
The term ‘ion’ was 1st used by English physicist and chemist Michael Faraday in 1834 after a suggestion by English Polymath, Scientist, William Whewell. Michael Faraday used this term for those species which were moving one electrode to another through an aqueous medium. The terms ‘anion’ and ‘cation’ are also coined by Faraday and Whewell. In 1884, Swedish scientist Svante Arrhenius explained that solid crystalline salts dissociate into paired charged particles when dissolved. For this, he won the Nobel prize in Chemistry in 1903.
What is an Ion?
The word ion is originated from the Greek word ἰόν, ion, which means ‘going’. Ions are charged species. An ion can be defined as an atom or molecule that has a net electrical charge. In an atom, the number of electrons and protons is equal so they possess zero charges or are neutral in nature. While in ions the number of protons is equal but the number of electrons is unequal. So, they possess either positive or negative charges. [Na^{+}, O^{-2}, NH_{4}^{+}, OH^{-}] etc. are examples of ions.
Ions which are a group of elements or atoms that are covalently bonded but carry either positive or negative charge are called polyatomic ions. [CN^{-}, OH^{-}, NH_{4}^{+}, NO_{3}^{-}, CO_{3}^{-2}] etc. are examples of polyatomic ions. Ions that have only one element that carries either a positive or negative charge are called monatomic ions. [Na^{+}, O^{-2}, Al^{+3}, Ce^{+3} ]etc. are examples of monatomic ions.
What is Cation?
Those ions which possess a positive charge are called cations. [Na^{+}, Al^{+3}, Ce^{+3} ] etc. are examples of cations. When an atom loses its electron/s then it gains a positive charge due to fewer electrons than protons in its nucleus. Then this positively charged species is called a cation. The term was coined by Faraday and Whewell. It is taken from the Greek word κάτω (káto) ἰόv (kation) which means ‘going down.
Keep in mind that the sign to denote cation is ‘+’ and is placed after the symbol and not before it. Based on the electron lost, a potassium atom is considered monovalent as it only loses one electron and thus has a 1+ charge. While Magnesium is considered as divalent as it loses 2+ electrons from its outermost orbit to form a stable octet. The elemental name is defined as the cation name.
What is Anion?
Those ions which possess a negative charge are called anions. [O^{-2}, CN^{-}, OH^{-}, Cl^{-}] etc. are examples of anions. When an atom gains electron/s to get stability, then it gains a negative charge due to more electrons than protons in its nucleus. Then this negatively charged species is called an anion. The term was coined by Faraday and Whewell. It is taken from the Greek word ἄνω ἰόv (anion) which means ‘going up.
Difference Between Cation and Anion
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S.No. |
Cation |
Anion |
|
1. |
An ion or a charged particle that has a positive charge is called a cation. An |
An ion or a charged particle that has a negative charge is called anion. |
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2. |
The word cation is originated from Greek word κάτω (káto) ἰόv (kation) the which means ‘going down. |
The word anion is originated from Greek word ἄνω ἰόv (anion) which means ‘going up. |
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3. |
In cations, the number of protons is more than the number of electrons. |
In anions, the number of electrons is more than the number of protons. |
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4. |
Generally, metals form cations. |
Generally, non – metals form anions. |
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5. |
Cations get attracted towards the negatively charged electrode in electrolysis. |
Anions get attracted towards the positively charged electrode in electrolysis. |
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6. |
Cations gain electrons and convert into neutral atoms or molecules. |
Anions generally lose electrons and convert into neutral atoms or molecules. |
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7. |
Cations from electrostatic or ionic bonds with anions form ionic compounds. |
Anions from electrostatic or ionic bonds with cations form ionic compounds. |
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8. |
[Na^{+2}, Mg^{+2}, Ca^{+2}, Fe^{+3}]etc. are examples of cations. |
[O^{-2}, Cl^{-}, Br^{-} ]etc. are examples of anions. |
This is all about the difference between cations and anions. If you are looking for solutions to NCERT Textbook problems based on this topic, then log on to the website or download Learning App. By doing so, you will be able to access free PDFs of NCERT Solutions as well as Revision notes, Mock Tests and much more.
Ion Chromatography:
Ion chromatography is used to analyze and separate both cations and anions in environmental samples. The separation of analytes on columns has resulted from the same analysis results in different separation procedures. Conductivity detectors are the most common type of detection here, where changes in ion-exchange affinities of distinct types of ions are detected. The most commonly utilized concept is reversible complexation, whereas, in irreversible complexation, the complex samples swap anions as and when r
equired.
Applications of Ion Exchange Resin:
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Water Softening: In this, the resins are used to replace the constituents found in hard water. The magnesium and calcium are replaced using sodium ions.
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Water Purification: In this, the resins are used to replace hazardous metal and poisonous ions from the solution. These components are replaced by sodium and potassium ions which are more innocuous.
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In Metal Separation: They are used to purify and separate metal from lanthanides. Except for highest-purity products, solvent extraction has mostly been used in ion-exchange resins.
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Catalysis: They also used organic synthesis. For scission of ether protecting groups and rearrangements reactions for acidic ion-exchange solid catalysts have been used.