Coordinate covalent bonds definition

Lewis (1923) put forward another definition of acids and bases solely dependent on giving or taking of an electron pair. According to Lewis— an add is an electron pair acceptor, whereas a base is an electron pair donor . Therefore, it is obvious that whenever any neutralization occurs the formation of an altogether new coordinate covalent bond between the electron pair donor and acceptor atoms take place. 

In the same year that Bronsted and Lowry proposed their definition of acids and bases, an American chemist named Gilbert Lewis proposed an alternative definition that not only encompassed Bronsted-Lowry theory but also accounted for acid-base reactions in which a hydrogen ion isn t exchanged. Lewis s definition relies on tracking lone pairs of electrons. Under his theory, a base is any substance that donates a pair of electrons to form a coordinate covalent bond with another substance, while an acid is a substance that accepts that electron pair in such a reaction. As we explain in Chapter 5, a coordinate covalent bond is a covalent bond in which both of the bonding electrons are donated by one of the atoms forming the bond. 

That being the case, it is appealing to refer to anion receptors as ligands. However, traditionally the commonly understood definition of ligand has been a Lewis base capable of forming a coordinate-covalent bond with a metal ion. Since for anions, the ligand actually behaves as a Lewis acid, the definition needs to be expanded to include both Lewis acid and Lewis base behavior. 

How would transition metal ions be classified using the Lewis definition of acids and bases What must a ligand have to bond to a metal What do we mean when we say that a bond is a coordinate covalent bond ... 

These definitions do not specify that an electron pair must be transferred from one atom to another—only that an electron pair, residing originally on one atom, must be shared between two atoms. Neutralization is defined as coordinate covalent bond formation. This results in a covalent bond in which both electrons were furnished by one atom or ion. 

In Section 10.4 we saw that the B atom in BF3 is xp -hybridized. The vacant, unhybridized 2p orbital accepts the pair of electrons from NH3. So BF3 functions as an acid according to the Lewis definition, even though it does not contain an ionizable proton. Note that a coordinate covalent bond is formed between the B and N atoms, as is the case in all Lewis acid-base reactions. 

In 1923, Gilbert Newton Lewis defined an acid as an electron pair acceptor and a base as an electron pair donor. This definition is even more inclusive than the previous one because it includes all Bronsted-Lowry acids and bases as a subset and provides the foundation for the field of coordination chemistry. A coordination compound is the product of a Lewis acid-base reaction, such as the one shown in Equation (14.11) and Figure 14.5, in which the metal ion (Lewis acid) and ligand (Lewis base) are held together by a coordinate covalent bond. 

In 1932 Gilbert Lewis proposed a more general definition of acids and bases. A Lewis acid is a species capable of accepting an electron pair to form a coordinate covalent bond and a Lewis base is a species capable of donating a pair of electrons to form a coordinate covalent bond. 

A complex is a molecule/ion containing a central metal atom/ion surrounded by a definite number of ligands held by secondary valences or coordinate covalent bonds. 

Searching for the property common to all acids, or that common to all bases, Lewis concluded that acids and bases correspond respectively to what Sidgwick later called acceptor and donor molecules. Neutralization is the formation of the coordinate covalent bond between the acid and the base. Such a definition... 

The original definition of the coordinate covalent bond apparently was not intended to imply any fundamental difference between it and any other covalent bond. The word coordinated was used merely to indicate an imaginary difference in the way the covalent bond is formed. 

In view of the controversies evident in the literature, it seems best to retain the original definition. A coordinate covalent bond is merely any covalent bond both electrons of which were originally supplied by one of the two atoms involved. Once such a bond is formed, there may be no way of distinguishing it from any other covalent bond. (One advantage of this definition is that it might render meaningless such controversies as the one between Samuel and Wheland. )... 

In view of this brief summary of the present situation, there seems to be no justification for the designation of coordinate covalent bonds by means of plus and minus signs. There is no difference warranting such a distinction between normaP and coordinate covalent bonds. The only difference is as stated in the original definition. A coordinate covalent bond is merely a covalent bond in which both electrons are thought of as being supplied by the same atom. 

By these definitions, OH , a Bronsted-Lowry base, is also a Lewis base because lone-pair electrons are present on the O atom. So too is NH3 a Lewis base. HCl, conversely, is not a Lewis acid It is not an electron-pair acceptor. We can think of HCl as producing H, however, and H is a Lewis acid. H forms a coordinate covalent bond with an available electron pair. 

Pauling offered the following definition of a chemical bond ... there is a chemical bond between two atoms or groups of atoms... (if) forces acting between them are such as to lead to the formation of an aggregate with sufficient stability to make it convenient for the chemist to consider it as an independent molecular species. Chemical bonds include ionic bonds, coordinate covalent... 

Lewis acid-base theory— To describe reactions where no proton transfer occurs, - Lewis has proposed a more general acid-base concept where an acid is a molecule or an ion with an incomplete outer electron sphere, i.e., an acceptor of electron pairs. A base is a molecule or an ion having a free electron pair, i.e., an electron pair donor. A neutralization reaction is characterized by the formation of a coordination or covalent bond. The following reactions illustrate the Lewis-definition ... 

Following the old definition by Sidgwick (from 1927) that the coordinate bond is a covalent bond formed by the donation of one pair of electrons from the donor atom (e.g. H, Cl ) or molecule (CgHg, ER3, etc.) to a complex centre, in the section on complexing (naturally including acidity and basicity) only species are considered that contain at least one dative-covalently bound ligand. This implies that neutral three- and five-coordinated species of the type R3E and R5E (E=As, Sb, Bi) have not been included. 

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