Introduction
Chemical bonding is one of the most important topics in chemistry because it explains how atoms combine to form molecules and compounds. As we have seen in covalent bonding, atoms can achieve stability by sharing electrons with one another.
However, not all covalent bonds are formed in exactly the same way.
In an ordinary covalent bond, each atom contributes one electron to the shared pair. But what happens when one atom supplies both electrons needed to form a bond?
This leads us to an interesting type of chemical bonding known as a dative covalent bond, also called a coordinate covalent bond.
Dative bonding is particularly important in understanding the formation of certain molecules and ions, such as the ammonium ion (NH4+), hydroxonium ion (H3O+), and complexes formed between metal ions and molecules.
In this article, we will explain the meaning of a dative bond, how it is formed, its characteristics, and common examples, using simple explanations and chemical diagrams to make the topic easier to understand.
What Is a Dative Covalent Bond?
A dative covalent bond is a type of covalent bond in which both electrons forming the shared pair are donated by one atom, while the other atom provides an empty orbital to accommodate the electron pair. It is also known as a coordinate bond or coordinate covalent bond.
In this type of bonding, the atom that supplies the electron pair is called the donor, while the atom that accepts the electron pair is called the acceptor.
For a dative bond to form:
- One atom must have a lone pair of electrons available for donation.
- The other atom must have an empty orbital or suitable electron-deficient region that can accept the electron pair.
- The donated electron pair is shared between the two atoms.
A dative bond is usually represented by an arrow pointing from the electron-pair donor towards the electron-pair acceptor.
For example:
A: → B
Here:
- A is the electron-pair donor.
- B is the electron-pair acceptor.
- The arrow shows the direction in which the electron pair is donated.
Important: Although both electrons are supplied by one atom during bond formation, the resulting bond is a covalent bond. Once formed, it behaves much like an ordinary covalent bond.
How Is a Dative Covalent Bond Formed?
A dative covalent bond forms when an atom with a lone pair of electrons donates that pair to another atom that can accept it.
Related Topics
* What is chemical combination?
* Differences between ionic (electrovalent) and covalent bonds
To understand this process, let us consider the formation of the ammonium ion. Nitrogen has five electrons in its outermost shell. In ammonia (NH3), nitrogen forms three covalent bonds with three hydrogen atoms, leaving one lone pair of electrons. This lone pair can be donated to a hydrogen ion (H+), which has no electrons.
When ammonia reacts with a hydrogen ion, the nitrogen atom donates its lone pair to the hydrogen ion, forming an ammonium ion (NH4+).
The reaction is represented as:
NH3 + H+ → NH4+
The coordinate bond can be represented as:
NH3: → H+
The nitrogen atom is the donor because it supplies both electrons, while the hydrogen ion is the acceptor.
After the bond is formed, all four nitrogen-hydrogen bonds in the ammonium ion are equivalent. The original coordinate bond cannot be distinguished from the other N–H bonds simply by their bond lengths or strengths.
Examples of Dative Covalent Bonds
There are several examples of compounds and ions in which coordinate covalent bonding occurs. Let us examine some important examples.
1. Formation of the Ammonium Ion (NH4+)
The ammonium ion is one of the common examples of a dative covalent bond.
Ammonia (NH3) contains a nitrogen atom bonded to three hydrogen atoms. Nitrogen has five valence electrons, out of which three are used to form covalent bonds with hydrogen atoms. The remaining two electrons form a lone pair.
When ammonia comes into contact with a hydrogen ion (H), the nitrogen atom donates its lone pair to the hydrogen ion.
The reaction is:
NH3 + H+ → NH4+
The newly formed bond between nitrogen and hydrogen is initially represented as a coordinate covalent bond because both bonding electrons come from nitrogen.
Key points:
- Electron-pair donor: Nitrogen atom.
- Electron-pair acceptor: Hydrogen ion (H+).
- Product formed: Ammonium ion (NH4+).
2. Formation of the Hydroxonium Ion (H3O+)
The hydroxonium ion is another important example of coordinate covalent bonding.
A water molecule (H2O) contains an oxygen atom bonded to two hydrogen atoms. Oxygen has six valence electrons and possesses two lone pairs after forming its two O–H bonds.
When water reacts with a hydrogen ion (H+), the oxygen atom donates one of its lone pairs to the hydrogen ion.
The reaction is represented as:
H3O + H+ → H3O+
The oxygen atom supplies both electrons required to form the new O–H bond.
Key points:
- Electron-pair donor: Oxygen atom in water.
- Electron-pair acceptor: Hydrogen ion (H+).
- Product formed: Hydroxonium ion (H3O+).
The hydroxonium ion is particularly important in aqueous chemistry because it represents the hydrated form of hydrogen ions in water.
4. Formation of Metal Complex Ions
Dative covalent bonding also occurs during the formation of complex ions. For example, copper(II) ions can combine with ammonia molecules to form the tetraamminecopper(II) complex ion.
The reaction can be represented as:
Cu2+ + 4NH3 → [Cu(NH3)4]2+
Each ammonia molecule donates a lone pair of electrons from its nitrogen atom to the copper(II) ion.
The copper ion accepts these electron pairs, forming coordinate bonds with the ammonia molecules.
Key points:
- Electron-pair donor: Nitrogen atoms in ammonia molecules.
- Electron-pair acceptor: Copper(II) ion.
- Product formed: Tetraamminecopper(II) complex ion.
This type of bonding is important in coordination chemistry, which deals with the formation and properties of complex ions and compounds.
Characteristics of Dative Covalent Bonds
Dative covalent bonds have several important characteristics that distinguish their formation from ordinary covalent bonds.
1. Both bonding electrons come from one atom: Unlike ordinary covalent bonding, where each atom contributes one electron, the donor supplies the complete electron pair.
2. A lone pair is required: The donor atom must possess an available lone pair of electrons.
3. An electron-pair acceptor is required: The accepting atom or ion must have an empty orbital or another suitable means of accepting the electron pair.
4. An arrow represents the bond: A dative bond is commonly represented by an arrow pointing from the donor atom towards the acceptor atom.
5. It is a type of covalent bonding: The donated electrons become shared between the two bonded atoms.
6. It can form molecules, ions and complex compounds: Examples include ammonium ions, hydroxonium ions and metal complex ions.
Difference Between Ordinary Covalent Bonds and Dative Covalent Bonds
Both ordinary covalent bonds and dative covalent bonds involve the sharing of electron pairs. However, they differ in how the shared electrons are supplied during bond formation.
Ordinary covalent bond | Dative covalent bond |
Each bonded atom contributes one electron to shared pair | One atom contributes |
It requires electron contributions from both bonding atoms | It requires an electron-pair donor and ecceptor |
It is usually represented by a straight line | It is often represented by an arrow |
Example: H-H in hydrogen | Example: formation of NH4+ |
An important point to remember: Once a dative covalent bond has formed, it is not necessarily weaker or different in nature from an ordinary covalent bond. In the ammonium ion, for example, all four N–H bonds become equivalent.
Difference Between Covalent and Dative Bond Formation in Ammonium
It is helpful to understand that the ammonium ion contains four nitrogen–hydrogen bonds, but its formation involves two stages.
- First, nitrogen forms three ordinary covalent bonds with three hydrogen atoms to produce ammonia (NH3).
- Secondly, nitrogen donates its lone pair to a hydrogen ion (H+), forming the fourth bond and producing NH4+.
This can be represented as:
NH3 + H+ → NH4+
Although one bond was formed through donation of a lone pair, all four N–H bonds in the resulting ammonium ion are equivalent.
Importance and Applications of Dative Covalent Bonding
Dative covalent bonding is important in several areas of chemistry.
1. Formation of complex ions: Coordinate bonds help metal ions combine with molecules or ions called ligands to form complex ions.
2. Acid-base reactions: The formation of ammonium and hydronium ions involves the donation of an electron pair to a hydrogen ion. This illustrates the Lewis acid-base concept.
3. Biological processes: Coordinate bonding is important in many metal-containing biological molecules and proteins. For example, metal ions in haemoglobin and other metalloproteins interact with surrounding molecules through coordination bonds.
4. Industrial chemistry: Coordinate bonding is involved in many catalysts and metal complexes used in industrial chemical processes.
5. Analytical chemistry: Complex formation is used in chemical analysis to identify and determine the concentration of certain metal ions.
Frequently Asked Questions (FAQs) About Dative Covalent Bonds
1. What is a dative covalent bond?
A dative covalent bond is a type of covalent bond in which both electrons in the shared pair are donated by one atom to another atom that can accept the electron pair.
2. What is another name for a dative bond?
A dative bond is also called a coordinate covalent bond or coordinate bond.
3. What are the conditions necessary for dative covalent bonding?
Two important conditions are required:
- One atom must have an available lone pair of electrons to donate.
- The other atom must have an empty orbital or a suitable electron-deficient region to accept the electron pair.
4. What is an example of a dative covalent bond?
The formation of the ammonium ion (NH4+) from ammonia (NH3) and a hydrogen ion (H+) is a common example.
NH3 + H+ → NH4+
5. How is a dative covalent bond represented?
A dative covalent bond is usually represented by an arrow pointing from the atom donating the electron pair towards the atom accepting it.
For example:
N → H
6. Is a dative bond stronger than an ordinary covalent bond?
Not necessarily. Bond strength depends on the atoms involved and their bonding environment. Once formed, a dative bond is a covalent bond and can have similar strength to an ordinary covalent bond.
7. What is the difference between a coordinate bond and an ionic bond?
A coordinate bond involves the sharing of an electron pair donated by one atom, whereas an ionic bond involves electrostatic attraction between oppositely charged ions.
Conclusion
A dative covalent bond is an important type of chemical bonding in which one atom supplies both electrons required to form a shared electron pair.
For this bond to form, there must be an electron-pair donor with an available lone pair and an electron-pair acceptor capable of receiving the pair.
Common examples include the formation of the ammonium ion (NH4+), hydroxonium ion (H3O+), and metal complex ions.
Understanding dative covalent bonding will help students develop a better understanding of chemical bonding, Lewis structures, acid-base reactions, and coordination chemistry.
If you are preparing for WAEC, NECO, JAMB, JUPEB, or other chemistry examinations, make sure you understand how the electron pair is donated and how to identify the donor and acceptor atoms in a coordinate bond.
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