Lewis Acid and Base

The Lewis theory of the acid-base reaction describes the lewis acid and base as the acceptor of electron-pair and donor of the electron pair, respectively. So, the Lewis base denotes a pair of electrons to the acid to form a byproduct consisting of the coordinate covalent bond. This product is known as the Lewis adduct. Acid and bases are the essential topics of Chemistry. The Lewis acid/base theme is one of the most widely used theories, and it goes beyond the H+ and OH- ions to define acids and bases. Apart from academics, we have also encountered several uses of acid and base in our daily life. So, go thoroughly through lewis acid and base study material to better understand the topic.

Lewis Acid

Lewis acids are chemical compounds with vacant orbitals, and they have the potential to accept the pair of electrons from the lewis bases. “Lewis” denotes the chemical species having the trigonal planar structure and a vacant p-orbital. BR3 is an example of such a category of Lewis acid. (here, R can be an organic substituent or a halide). Some compounds such as water are known as both Lewis bases and acid as they can donate and accept the electron pairs depending on the type of reaction. 

Examples of the Lewis Acids

Many reactions involve Lewis acids and bases. Some common examples of Lewis acids that can acquire electron pairs are:-

• H+ ions (or protons) can be considered Lewis acids, and the cations of d block elements that portray states of high oxidation act as an electron-pair receiver. An example of such an element is Iron (Fe2+ and Fe3+).
• Cations of metals like Li+ and Mg2+ make coordination compounds with the water as the ligand. These aqua compounds can receive electron pairs & acts as Lewis acids.
• CH3+ and other trigonal planar species produce carbocations that take electron pairs.
• Lewis acids can be made from the pentahalides of the following group 15 elements: antimony, arsenic, and phosphorus.
• Cations of d block elements that portray states of high oxidation
• Copper (Cu)
• Hydrogen (H+) ions with the onium ions (H3O+)

Any electron-deficient system, such as enones, can act as an acceptor of electron pairs in addition to the chemical compounds listed above.

Lewis Base

A Lewis base is an electron-pair donor. It is a compound that donates a pair of electrons to form a covalent bond. According to this definition, a Lewis base is a nucleophile. The transfer of paired electrons from a base to an acid medium represents the Lewis acid-base reaction. We can conclude from the above reaction that this pair of electrons is nonbonding to acids. Nonbonding electrons are a type of loose change that occurs. Due to its lack of electrons, a hydrogen ion can receive a pair of electrons.

The most popular Lewis bases are alkylamines, ammonia, and other amine groups. Lewis bases are anionic, and the pKa of the parent acid determines the strength of their base. Lewis bases can be categorised as nucleophiles since they are electron-rich entities with the ability to contribute electron pairs. Lewis acids are classified as electrophiles.

Examples of Lewis Bases

As we have read above, Lewis bases are the chemical compounds or elements that can donate an electron. Some of the most common examples of Lewis base are:-

• Pyridine and its derivatives can donate their electron pairs. Hence, it is classified as the Lewis base. 
• The compounds in which elements belong to group 16 of the Periodic table, such as Tellurium, Sulphur, Oxygen, and Selenium, exhibit oxidation states of -2 are known as Lewis Bases. Ketones and water compounds are examples of such groups. 
• The simple anions with the electron pair act as Lewis bases by denoting the extra electrons. Some complex anions like sulphate anion (SO42-) can donate their electron pair. The other common examples of these anions are H– and F–.
• The π-systems such as ethene, benzene, and ethyne are also rich in electrons and exhibit electron-donating capabilities. 
• The weak Lewis acids have strong conjugate Lewis bases. Aside from that, due to their electron pair donating capacities, several chemical species with a lone pair of electrons, such as CH3– and OH–, are classified as Lewis bases.

Some of the common examples of Lewis bases are 

• H2O
• SbCl5
• C2H2
• I–
• NH3
• F–
• CH3–
• H–
• Cl–
• SO42-

Chemical Reactions between Lewis Acid and Base

When it comes to the Lewis concept of acid-base reactions, bases are known for contributing electron pairs, while acids accept those electron pairs. As a result, a Lewis acid can be any compound, such as an H+ ion, that accepts nonbonding pairing electrons. To put it another way, Lewis acid is an electron-pair acceptor. An ion of OH–, on the other hand, can be the best Lewis base because it contributes a pair of nonbonding electrons. A Lewis base is thus an electron-pair donor.

Conclusion

We have studied the definition, properties, applications, and examples of Lewis Acids and Bases in the above notes. Lewis acids and bases are electron-pair acceptors and electron-pair donors, respectively. As a result, a Lewis base can transfer two electrons to a Lewis acid, resulting in a product with a coordinate covalent bond. If you are preparing for the upcoming IIT JEE or NEET examination, you can prefer these study material notes on lewis acid and base to better understand the concepts.