Co-ordinate covalent bond-definition-examples-formation conditions.

Co-ordinate covalent bond definition in chemistry

If one of the two participating atom in a chemical attachment, provide one pair of electrons and both they complete their octet by sharing this electron pair, then the 

power of the two participating atom for the attachment to each other, is called co-ordinate covalency.

The chemical bond which  is created due to co-ordinate covalency is called co-ordinate bond.The co-ordinate bond is also called dative bond.

Although co-ordinate bond is also one type of covalent bond. But this bond is polar in nature. Because, the donor atom gets positive charge and the acceptor atom gets negative charge.

Like covalent bond, co-ordinate bond is also produced by the overlapping of two atomic orbital .

Since the atomic orbital has a specific direction , hence co-ordinate bonds are also have a specific direction.

What is co-ordinate covalency?

If one of the two participating atom in a chemical attachment, provide  one pair of electrons and both they complete their octet by sharing this electron pair, then the 

power of the two participating atom for the attachment to each other, is called co-ordinate covalency.

Co-ordinate covalent  bond examples .

There are many examples of co-ordinate covalent bond or co-ordinate covalency .

Such as , NH₃.BF₃ , LiAlH₄ , NaBH₄, NH₄Cl, Al₂Cl₆  etc compounds contain co-ordinate covalent bond .

Formation of co-ordinate  covalent compound, like NH₃.BF₃ is shown below . 

The nitrogen atom in ammonia have one lone pair of electrons . On the other hand, the boron atom in BF₃ molecule have incomplete octet.So B-atom have a tendency to gain two electrons for completion of its octet.

Hence, in reaction between ammonia and boron tri-fluoride, ‘N’-atom of ammonia molecule acts as electron donor and ‘B’-atom in BF₃ acts as electron acceptor.

But  both they complete their octet by sharing of electron pair equally . In this way , NH₃ and BF₃ molecule form a co-ordinate covalent bond to each other, resulting in the formation an adduct compound. 

Now, the molecules or ions which give up electron pair, they are called Lewis base and the molecules or ions which accept electron pair, are called Lewis acid. Hence, here NH₃ acts as a Lewis base and BF₃ acts as a Lewis acid.

Co-ordinate covalent bond formation conditions 

( I ) Between the two participating atoms, the donor atom must have one lone pair of electron.

( II ) The acceptor atom must have a vacant orbital so that the atom can accept the lone pair of electrons.

 ( III ) The complete displacement of electrons from donor atom to acceptor atom does not occur. Both the atom ( donor and acceptor ) shall be use the electron pair equally.

Characteristics of co-ordinate covalent compounds .

Co-ordinate covalent bond is one type of covalent bond. So the characteristics of co-ordinate covalent compounds are similar to that of covalent bond .

( I ) Co-ordinate covalent compounds may be solid, liquid or gaseous in room temperature .

 ( II ) Co-ordinate covalent compounds are polar in nature. Actually Co-ordinate covalent bond is more polar than covalent bond and less polar than ionic bond.

Consequently, the melting and boiling point of Co-ordinate covalent compounds are higher than covalent compounds but less than ionic compounds.

(III ) Co-ordinate covalent compounds have a co-ordinate covalent bond . But all other bonds are covalent bond.

Hence  Co-ordinate covalent compounds are soluble in non-polar solvent ( benzene , carbon disulfide, carbon tetrachloride etc )but the solubility in polar solvent is very much less .

( IV ) Compounds with co-ordinate covalent bond does not ionize in aqueous solution as well as in melting condition.So they can not conduct electricity.

( V)  Co-ordinate covalent  bond is rigid and they have specific direction . So co-ordinate covalent compounds show isomerism properties .

Why does AlCl₃ exist as a diner ?

The chlorine atom in AlCl₃ molecule have three lone pair of electrons . On the other hand, ‘Al’-atom have incomplete octet .

So ‘Al’-atom have a tendency to gain two electrons for completion of its octet.

Hence, Cl-atom of one AlCl₃ molecule donate electron to the Al-atom of another AlCl₃ molecule and form a co-ordinate bond.

But  both they complete their octet by sharing of electron pair equally . In this way , two AlCl₃ molecule form a co-ordinate covalent bond to each other, resulting in the formation of a dimer molecule Al₂Cl₆ . 

Now, the molecules or ions which give up electron pair , they are called Lewis base and the molecules or ions which accept electron pair , are called Lewis acid.

Hence, here chlorine atom acts as a Lewis base and ‘Al’-atom acts as a Lewis acid.

Why BCl₃ trigonal planar but AlCl₃ tetrahedral?

Boron atom in BCl3 molecule is sp2 hybridized. Three half filled hybridized orbital of ‘B’-atom is overlapping with the three half filled p-orbital of ‘Cl’-atom ,resulting in the formation of trigonal planar BCl₃ molecule .

Boron atom can not attach with four chlorine atom due to its small size .Hence, the geometry of BCl₃ molecule is trigonal planar.

On the other hand, chlorine atom in AlCl₃ molecule have three lone pair of electrons and ‘Al’-atom have incomplete octet. So ‘Al’-atom have a tendency to gain two electrons for completion of its octet.

Hence, ‘Cl’-atom of one AlCl₃ molecule donate electron to the ‘Al’-atom of another AlCl₃ molecule.

 In this way, two AlCl₃ molecule form  a co-ordinate covalent bond to each other, resulting in the formation of a dimer molecule Al₂Cl₆. For this reason, the shape of AlCl₃ molecule is tetrahedral.

Summary

• Co-ordinate covalent bond definition in chemistry 
• What is co-ordinate covalency ?
• Co-ordinate covalent  bond examples .
• Co-ordinate covalent bond formation conditions .
• Characteristics of co-ordinate covalent compounds .
• Why does AlCl3 exist as a diner ?
• Why BCl3 trigonal planar but AlCl3 tetrahedral ? 

Ionic bond definition examples properties.