Dative_bonds

Dative_Bonds

What a Dative Bond is:

A dative bond, otherwise known as a coordinate covalent bond, is a terminology that specifies that "origins" of shared electrons between two atoms as coming from the same atom. Note: Although the term "dative bond" may seem to describe a form of bonding, this is not the case; dative bonds hold no distinction from regular covalent bonds.

How Dative Bonds work:

Dative bonds are formed when one molecule donates an electron pair (Lewis base) and another molecule accepts the donated electron pair (Lewis acid). This sharing of electrons results in a positive formal charge for the Lewis base and a negative formal charge for the Lewis acid.

Why Dative Bonds are appropriate:

The "goal" for the atom is to create stable octet, or complete valence shell, state. Some atoms, however, may use all of their valence electrons without actually forming an octet.

Example: BH3
H
|
B— H
|
H

Conversely, other atoms may complete their octets without sharing all of their valence electrons with other atoms (unshared pairs)

Example: NH3
H
|
N—H
|
H

And when a Lewis base and a Lewis acid meet, a stable covalently bonded molecule forms.

Example: H3NFC:+BFC:-H3 -> NH3BH3
.......H H
.........| |
.H—B:N—H
.........| |
.......H H

Frame 33

Using dative bonds, Lewis was able to explain that the pentavalence exhibited by some nitrogen atoms, such as that in NH4Cl, is actually tetravalence and an electrostatic attraction between charged particles. For example, the nitrogen in NH4Cl has a dative bond with a proton, resulting in a positive charge on the NH4+. The positive charge on NH4+ then forms an electrostatic attraction with the negative charge on a Cl- ion, creating the "pentavalent" nitrogen.

Frame 34

Examples of dative bonding:

1. The nitrogen atom in an amine donates an electron pair to an oxygen atom to form an amine oxide. As a result, the nitrogen gains a positive formal charge, while the oxygen gains a negative formal charge.

2A. The sulphur atom in a sulphide donates an electron pair to an oxygen atom to form a sulphoxide. As a result, the sulphur gains a positive formal charge, while the oxygen gains a negative formal charge.

2B. The sulphur atom in a sulphoxide donates another electron pair to an oxygen atom to form a sulphone. As a result, the sulphur gains another positive formal charge (+2), while the oxygen gains a negative formal charge.

Sources

1. McBride, Michael. Freshman Organic Chemistry. Sterling Chemistry Lab, New Haven, 5 September 2008.

2. Coordinate Covalent Bond. 2 September 2008. Wikipedia: The Free Encyclopedia. 6 September 2008. < external link: http://en.wikipedia.org/wiki/Coordination_bond>.

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