Coordinate Bond
Coordinate Bond
A coordinate bond, also known as a dative covalent bond, is a type of chemical bond where both electrons in the bond are contributed by the same atom. This is in contrast to a typical covalent bond, where each atom contributes one electron to the bond pair.
Formation of Coordinate Bonds
A coordinate bond is formed when a Lewis base donates a pair of electrons to a Lewis acid. A Lewis base is an electron pair donor, while a Lewis acid is an electron pair acceptor.
For example, in the formation of the ammonium ion ((NH_4^+)), the nitrogen atom in ammonia ((NH_3)) has a lone pair of electrons. When it encounters a hydrogen ion ((H^+)), which lacks electrons, the nitrogen atom can donate its lone pair to form a bond with the hydrogen ion, resulting in a coordinate bond.
Representation
In Lewis structures, a coordinate bond is typically represented by an arrow (( \rightarrow )) pointing from the donor atom to the acceptor atom. For example:
:N → H+
Characteristics of Coordinate Bonds
- Electron Pair Origin: Both electrons come from the same atom.
- Bond Strength: Coordinate bonds are generally as strong as covalent bonds.
- Polarity: The bond can be polar if the electronegativity difference between the donor and acceptor is significant.
- Reactivity: The reactivity of coordinate bonds can vary depending on the nature of the donor and acceptor atoms or groups.
Differences Between Coordinate and Covalent Bonds
Here is a table summarizing the differences between coordinate bonds and covalent bonds:
| Feature | Coordinate Bond | Covalent Bond |
|---|---|---|
| Electron Source | Both electrons from one atom | One electron from each atom |
| Representation | Arrow (( \rightarrow )) | Dash (( - )) |
| Example | (NH_4^+) | (H_2) |
| Bond Formation | Lewis acid-base reaction | Mutual sharing of electrons |
| Reversibility | Often reversible | Typically irreversible |
Examples of Coordinate Bonds
Ammonium Ion ((NH_4^+)):
- Nitrogen in ammonia ((NH_3)) donates its lone pair to a proton ((H^+)).
Metal Complexes:
- Ligands such as water ((H_2O)) or ammonia ((NH_3)) donate electron pairs to metal ions to form complex ions, e.g., ([Cu(H_2O)_6]^{2+}).
Sulfur Dioxide ((SO_2)):
- One of the oxygen atoms donates a pair of electrons to the sulfur atom to form a coordinate bond.
Coordinate Bond in Complex Ions
Complex ions are species where a central metal ion is surrounded by ligands, which are molecules or ions that can donate a pair of electrons. The metal ion acts as a Lewis acid, while the ligands act as Lewis bases. The resulting coordinate bonds are crucial for the stability of the complex ion.
For example, in the hexaaquacopper(II) ion, ([Cu(H_2O)_6]^{2+}), each water molecule donates a pair of electrons to the copper ion, forming six coordinate bonds.
Conclusion
Coordinate bonds are an essential concept in chemistry, particularly in the study of complex ions and acid-base reactions. Understanding the nature of these bonds, how they form, and their properties is crucial for a comprehensive understanding of chemical bonding and reactivity.
For exam preparation, it is important to be able to identify and represent coordinate bonds, understand the differences between coordinate and covalent bonds, and recognize examples of coordinate bonds in various chemical species.