Lewis Acid and Base: Definition, Examples, Chemical Reactions & Applications

Divya Kare | Updated: Jul 5, 2022 22:xvi IST

Some chemical species tend to donate the pair of nonbonding electrons, and some tend to accept them. The species that accepts these electrons is known as a Lewis acid, while the specie that donates them is known as a Lewis base. There are several examples of Lewis acids and bases that we utilize in our day-to-24-hour interval lives.

In this article, we will talk over Lewis acid and base, their examples, chemical reactions and applications, etc.

Lewis Acid and Base

N. Lewis, in 1923, identified acids and bases based on their power to donate or accept a pair of electrons to form a covalent bail. For this, he gave a generalized definition of acid-base behaviour. When a Lewis acid and base bond together to form a molecule, it is known as a Lewis adduct.

Co-ordinate to Lewis concept of acid and base, we take the following definitions of Lewis acid and base:

Lewis Acid

Whatever chemical substance which has empty orbitals and tin accept a pair of electrons is known every bit a Lewis acrid. Classically, this term was used to define chemical substances with an empty p-orbital and a triangular planar construction. For instance, \(BF_3 \) is such a Lewis acid.

Some examples of a Lewis acrid are as follows:

  1. Copper (Cu)
  2. \(H^+\) ions (or protons) forth with \(H_3O^+\)
  3. \(Fe^{2+}\), \(Fe^{iii+}\) or cations of d-block elements act every bit electron-pair acceptors and display high oxidation states.
  4. Cations of some metals like \(Li^+\) and \(Mg^{2+}\).
  5. Penta halides of Antimony, Arsenic and Phosphorus.
  6. Besides these chemical species, whatsoever electron-deficient π-system can take electron pairs, for example, enones.

Lewis Base of operations

Whatsoever chemical substance which can donate a pair of electrons and has a highly localized HOMO (The Highest Occupied Molecular Orbital) is known equally a Lewis base. Ammonia is the almost common example of a Lewis base.

Some examples of a Lewis base are as follows:

  1. \(H_20\)
  2. Pyridine and its derivatives.
  3. \(Cl^-, l^-, F^-, H^-, CH_3^-\)
  4. The chemical compounds contain Oxygen, Sulphur, Selenium, and Tellurium with a -2 oxidation state.
  5. The π-systems that are rich in electrons.

How To Identify Lewis Acid And Lewis Base

To identify whether a chemical species is a Lewis acid or base of operations, we can consider the post-obit two weather:

  1. If the valence shell of the chemical compounds' central atom is filled, it will take the electron pair and will act as a Lewis acrid.
  2. If the primal atom of the chemic chemical compound has any pair of electrons not bonded, it will donate that pair and volition act equally a Lewis base.

For example: In the case of aluminium bromide, aluminium has no unbonded electrons, and so it volition accept electrons and human action every bit a Lewis acid. But, in the case of ammonia, nitrogen has three electrons not bonded, so information technology volition donate them and act as a Lewis base of operations.

Chemic Reactions between Lewis Acid and Base

Diverse chemical reactions involve Lewis acrid and base. These are as follows:
1) Reaction between Ammonia and Silver cation:
\(NH_3 + Ag^+ \longrightarrow Ag(NH_3)_2^+ \)

In this reaction, argent cation acts equally a Lewis acid while ammonia acts as a Lewis base.
ii) Reaction between \(H^+\) and \(H_2O\):
\(H^+ + H_2O \longrightarrow H_3O^+ \)

In this reaction, \(H^+ \) acts equally a Lewis acid while \(H_2O\) acts as a Lewis base.
iii) Reaction between Boron Trifluoride and Fluoride Ion:
BF3 + F- —> BF4- \( BF_3 + F^- \longrightarrow BF_4^- \)

In this reaction, Boron Trifluoride acts every bit the acceptor of the electron pair donated by the fluoride ion.

Difference Between Lewis Acid And Base

Following are the differences betwixt Lewis acrid and base:

Lewis Acid Lewis Base
1. Lewis acid accepts electron pairs i. Lewis base donates electron pairs.
2. They act as electrophiles. 2. It acts as nucleophiles.
3. All metal ions or atoms deed as Lewis acids. three. All anion ions human activity every bit Lewis bases.
iv. Due to its empty d-orbitals, molecules in which the central cantlet expands are Lewis acids. 4. All metal oxides that have no d-orbitals are Lewis bases.
5. Examples: \(H^+, Cu^+, Zn^+, FeCl_3 \) 5. Examples: \(Cl^-, NH_3, H_2O\)

Application Of Lewis Acrid And Base

Following are the applications of Lewis acid and base:

  1. Lewis acids act as a catalyst in many reactions like in the Friedel-Crafts reaction – \(AlCl_3\) accepts a lone pair of electrons which belongs to the chloride ion leading to \(AlCl_4^-\) formation. The chemical reaction for this can be written as follows:

\(AlCl_3 + RCl \longrightarrow AlCl_4^- + R^+ \)

  1. Lewis acids are besides widely used to encourage many cationic or pseudo-cationic chemic reactions.
  2. Lewis acid's activity tin can be seen in photochemical (\(CO_2\) reduction), electrochemical and hydrogenation,
  3. Lewis bases are used to strengthen the action and selectivity of metal catalysts and are used equally ligands in coordination chemical science.
  4. Chiral Lewis bases are oftentimes used to confer chirality on catalysts, to enable asymmetric catalysis,

And so, this concludes the topic of Lewis acid and base. To study more such chemistry topics, download the Testbook App, which will aid you with your exam preparation. You can notice more study material on this app, such as revision notes, sample papers, mock tests, etc.

Lewis Acid And Base FAQs

Q.1  What is a Lewis base?

Ans.1 Equally per the Lewis acid and base concept, a Lewis base is a species that donates a pair of nonbonding electrons, or we tin can say that it is an electron-pair donor. For instance, \(NH_3\) and \(H_2O\) act as Lewis bases.

Q.2  Is NaCl a Lewis acid?

Ans.two NaCl is a neutral salt, so it is not a Lewis acrid. It is because of the fact NaCl has no vacant orbitals

Q.3 Why is Boron Fluoride a Lewis acid?

Ans.3 The electronic configuration of Boron in \(BF_3\) is \(1s^22s^22p^1\) which means that it has a vacant p-orbital. All of this indicates that \(BF_3\) is an electron-deficient species, so information technology behaves similar a Lewis acid.

Q.four What are the types of Lewis acrid?

Ans.4 Equally per HSAB theory, there are 2 types of Lewis acid; hard and soft acids. Hard acids are not very polarizable and accept a high charge density. Soft acids are more than polarizable and have a low accuse density.

Q.5  Is Boron Trichloride a Lewis base of operations?

Ans.v Stearic acids are proven to be good for the skin. These are emulsifiers, lubricants and emollients that help in softening the skin. It is because some natural sources that contain these acids, such as shea butter and coconut oil, have anti-inflammatory and moisturising properties.

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