A donor-acceptor bond, or coordination bond, is a type of covalent bond. We will identify the distinctive features of this type of connection, give examples that demonstrate its formation.
Covalent bond
First, we distinguish the distinctive features of the most covalent chemical bonds.
It can be polar and non-polar, depending on the position of the electron pair between the atoms. If a partial shift of the electron density toward one of the atoms occurs, a covalent polar chemical bond arises . A similar phenomenon is possible when a bond is formed between non-metals having different electronegativity. With its increase, a significant shift of the electron pair toward the atom with a large EO is observed. When a bond is formed between non-metals having the same value of electronegativity, there is no shift in the pair of electrons, this connection is called non-polar.
Examples are oxygen, hydrogen, ozone, phosphorus. The polar bond is hydrochloric acid, water, ammonia.
There is a special term due to which it is possible to characterize the number of electron pairs formed between atoms.
Given that the formation of one bond requires two electrons, there will be three bonds between the nitrogen atoms, that is, the multiplicity corresponds to three. Donor-acceptor bond is a special case of covalent polar bond, but intermolecular interaction of substances is assumed.
Mechanism features
For the formation of the usual covalent bond, an interaction between two electrons (a common pair) is sufficient. A chemical donor-acceptor bond is formed as a result of a pair of electrons on one side (from the donor), an unfilled (free) orbital from another atom (acceptor). In the case of a covalent polar (nonpolar) bond and during donor-acceptor interaction, the electrons eventually become common.
Formation of Ammonium Cation
How is a donor-acceptor bond formed? Examples of substances taught in high school chemistry are limited to ammonium cation. We will analyze his education in more detail.
Nitrogen, which is part of the ammonia molecule, is in the fifth group (main subgroup) of the periodic table. At its external energy level are five electrons. In the formation of an ammonia molecule, nitrogen spends three electrons on a covalent polar bond; therefore, an electron pair that does not participate in such a process remains unused.
It is she who gives him the right to exhibit the properties of a donor when ammonia molecules approach water dipoles. The hydrogen cation does not have its own electrons in water; therefore, it exhibits acceptor properties.
At a time when ammonia molecules are at a fairly close distance with hydrogen protons from water, a nitrogen cloud consisting of two electrons appears in the sphere of attraction of the hydrogen cation, it becomes common to them. As a result, a tetravalent bond is formed between nitrogen and hydrogen; a donor – acceptor mechanism is assumed. This is what is called a classic example of the formation of communication.
Oxonium cation formation
In the school curriculum (basic level), the oxonium cation (hydroxonium) is not considered, since the protolytic theory of solutions is studied only at a profile level. Since a donor – acceptor bond is also used here, we consider the examples of its formation in more detail.
In this case, a water molecule will act as a donor, and a proton exhibits acceptor properties. The donor-acceptor mechanism under consideration is what is called the basis of the chemistry of complex compounds, and therefore deserves special attention. He explains the essence of the theory of electrolytic decomposition of acids, salts, and bases when dissolved in water into cations and anions.
When forcing such a bond, bound electrons penetrate into the outer shell of the atoms they bind. In this case, there is an increase in the number of electrons in the outer shells by one.
The second communication formation algorithm
There is another mechanism by which a donor-acceptor bond is formed. Examples of such an interaction are numerous, in particular the formation of metal fluorides. The use of a pair of electrons of one of the reacting atoms is observed. As a result, one atom supplements its shell to the maximum amount, but far from all eight electrons take part in the bond, only a certain part of them. Those electrons that will not take part in the connection are called free, and with the help of the rest, a donor-acceptor bond is created. Examples of such a variant of a donor-acceptor bond relate to the formation of fluorides of alkali and alkaline earth metals. For example, sodium, potassium, and calcium fluoride are obtained in a similar manner.
What is the difference between a donor-acceptor bond? Stable compounds can be distinguished due to a similar mechanism of the formation of chemical compounds. For example, the dissolution of hydrogen fluoride in water, the bond between ammonia and aluminum chloride, leading to the formation of complex compounds.
Conclusion
Given the rules of donor – acceptor interaction, we note that inert gases may well act as active donors, since they have the maximum number of electrons on the outer shell. Experimentally, such a statement was fully confirmed, and inert gas oxides formed precisely by donor-acceptor interaction were detected.
This kind of covalent bond is of particular importance in human life. In addition to active participation in his life, thanks to donor-acceptor communication, it is possible to create food products and various pharmaceuticals. For example, the mechanism of formation of ammonium cation discussed above concerns the formation of ammonia, which is widely used in modern medicine.