Co-ordinate Bond

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Chemical compounds are generally formed by a force of attraction between the atoms or molecules or ions. This force of attraction is referred to as the chemical bond. The chemical bond keeps the atoms together in the resulting compound. Chemical bond accounts for the stability of a chemical compound. The stronger the bond, the greater is the stability of the compound. It is also true that the compounds are less stable and highly reactive if the chemical bond between the atoms is weak. In order to attain stability, the atoms either lose or gain energy. Chemical bonds can also be defined as the attractive force that binds two or more atoms together. The different types of chemical bonds are:

  1. Covalent bond

  2. Ionic bond

  3. Hydrogen bond

  4. Polar bond


What is Coordinate Bond Definition?

A coordinate bond is a special type of covalent bond. It can be defined as an alternate covalent bond in which the electron pair is shared from one atom only. In other words, both the electrons that form the shared pair are from the same atom. The coordinate bonds can also be alternatively referred to as Dative bonds or dipolar bonds. Coordinate bond is also at times referred to as Coordinate Covalent bond because it is a unique kind of covalent bond. We can visualize coordinate covalent bonds in the reactions that involve two non-metals such a hydrogen atom. It is also formed in the reactions involving metal ions and ligands.


Characteristics of Coordinate Covalent Bond

  • In coordinate bonding, the donor is the atom that shares a pair of electrons from itself to the other atom. 

  • The acceptor or receptor is the atom that receives the electron pair shared by the donor to attain stability. 

  • The coordinate bond is represented by a small line segment with an arrow pointing the acceptor indicating the direction of the sharing of the electron pair. The symbol used is ‘→’.

  • By sharing and receiving the electron pair, the donor and acceptor attain stability. 

  • The coordinate bonding corresponds to the Lewis theory of chemical bonding. 

  • It is easy to write the structures of complex organic molecules with a thorough understanding of the formation of coordinate covalent bonds.


Coordinate Bond Examples

There is a wide range of chemical compounds that we use in our day to day life which are formed by coordinate bonds. A coordinate bond involves the sharing of electrons from one atom only. The other atom just receives the shared electron pair. The direction of sharing is indicated by an arrow. If the coordinate bond is formed between the atoms X and Y, X, being the donor and Y, the receptor, the chemical compound with its bond is represented as:

X → Y


A Few Coordinate Bond Examples are

  1. Formation of Ammonium ion

  2. Formation of Hydronium ion

  3. Formation of Ammonia boron trifluoride


Formation of Ammonium Ion

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The above figure indicates the formation of covalent coordinate bonds during the formation of ammonium ions. The nitrogen atom in Ammonia shares its pair of electrons with the hydrogen ion to make it stable. Hence, the hydrogen atom is the donor in this case. However, the hydrogen ion (H+) ion receives the shared pair of electrons and hence is an acceptor. An arrow pointing towards the Hydrogen atom indicates that the electron pair is shared by nitrogen and accepted by hydrogen.


Formation of Hydronium Ion

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It is clearly indicated in the above representation that one pair of electrons from the oxygen atom of the water molecule is shared with the hydrogen ion to give the hydronium ion (H3O+). Here, the water molecule (H2O) is the donor and the hydrogen ion (H+) is the acceptor.


Formation of Ammonium Boron Trifluoride

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The Ammonium Boron Trifluoride is formed by the sharing of electrons by the Nitrogen atom in Ammonia (NH3) with the Boron atom in Boron Trifluoride (BF3). Here Ammonia is the donor and Boron trifluoride is the acceptor. The arrow towards Boron indicates that the pair of the electron is shared by ammonia with the boron. 


Properties of Coordinate Compounds

  1. The compounds that are coordinate bond examples have relatively lower melting and boiling points in comparison to the ionic compounds.

  2. Some coordinate compounds showcase isomerism.

  3. A coordinate bond is a directional bond because the sharing of electrons takes place in a specific direction.

  4. Coordinate bonds are weaker than Ionic bonds. 


Fun Facts

  • A coordinate covalent bond is also called the dative bond or dipolar bond.

  • Though the electron pair is completely shared by one atom during the formation of a coordinate bond, it is not identical to the ionic bond because neither of the atoms is completely losing or gaining electrons. 

FAQ (Frequently Asked Questions)

1. How Are Coordinate Covalent Bonds Different from Covalent Bonds?

  • A covalent bond is formed by mutual sharing of electrons (i.e. both the atoms involved in the bond formation share one electron each) whereas, a coordinate bond is formed by the sharing of electrons by one atom only. 

  • Covalent bonds are formed between two similar or dissimilar atoms. However, coordinate bonds are formed only between unlike atoms. 

  • Covalent bonds may be polar or nonpolar. But, coordinate bonds are always polar because they are formed between two, unlike atoms. 

  • The shared pair of electrons is denoted by a short line (-) in covalent bonds and the same is denoted by an arrowhead indicating the direction of the sharing of the electron pair (→) in coordinate bond.  

  • Covalent compounds are insoluble in water whereas coordinate compounds are sparingly soluble in water. 

2. What Are the Differences Between the Coordinate Bond and Ionic Bond?

Ionic bonds are formed by the electrostatic force of attraction between the positively charged cations and the negatively charged anions. However, though the electron pair shared by one atom only in case of coordinate bond formation, it does not involve the formation of ions because none of the atoms lose or gain electrons completely.