Main Difference – Covalent Bond vs Coordinate Bond
A chemical bond is the attachment of two atoms through exchanging electrons. This can be either through sharing electrons or through complete removal of electrons. A chemical bond always has a pair of electrons that have opposite spins. This electron pair is called a bond pair. Covalent bonds and coordinate bonds are chemical bonds that are formed as a result of sharing electrons between two atoms. A covalent bond is formed when both atoms share their electrons. But a coordination bond is formed when one atom donates one of its extra electron pairs to another atom. However, after the formation of the bond, both covalent bond and the coordinate bond seems identical. The main difference between covalent and coordinate bond is that both atoms in a covalent bond contribute to the formation of bond whereas only one atom in a coordination bond contributes to the formation of the bond.
Key Areas Covered
1. What is a Covalent Bond
– Definition, Formation, Examples
2. What is a Coordinate Bond
– Definition, Formation, Examples
3. What are the Similarities Between Covalent and Coordinate Bond
– Outline of Common Features
4. What is the Difference Between Covalent and Coordinate Bond
– Comparison of Key Differences
Key Terms: Bond Pair, Coordination Bond, Coordination Compound, Covalent Bond, Lone Pair, Valency
What is a Covalent Bond
A covalent bond is a type of chemical bond that is formed when two atoms share their unpaired electrons with each other. A covalent bond can be formed between two atoms of the same element or different elements. Most often, these covalent bonds are found in between nonmetals. Two atoms are more likely to share electrons when the electronegativities of those atoms are approximately similar.
Atoms tend to share their electrons when there are unpaired electrons in their outermost orbitals. Sometimes, atoms share electrons to obey the octet rule that indicates stability. However, this electron sharing leads to the formation of new compounds that are composed of atoms in different combinations. According to the valency of a particular atom, the number of covalent bonds it can form may vary.
A covalent bond can be either a sigma bond or a pi bond. A sigma bond is a single bond, which is composed of one electron pair. A double bond is composed of one sigma bond and one pi bond. Both bonds are covalent bonds.
Figure 1: Structure of H2O Molecule
In order to form a covalent bond, both atoms should contribute in equal amounts. Therefore, one electron from each atom should participate in order to form a single bond. For the formation of a double bond, two electrons from each atom are donated.
A covalent bond can be either polar or nonpolar bond depending on the electronegativity of each atom. If the difference of electronegativities between two atoms is very low (less than 0.4) or zero, it forms a nonpolar covalent bond. If the difference in electronegativities of two atoms is higher (0.4-1.7), then it is a very polar covalent bond.
What is a Coordinate Bond
A coordinate bond is a type of chemical bond that is formed due to the donation of a lone electron pair by one atom to another atom. Here, the lone electron pair is shared by two atoms. This occurs between an atom that is rich with electrons and an atom that is deficient in electrons. The electron-rich atom will donate a pair of electrons to the electron deficient atom. However, after the formation of the coordinate bond, it looks identical to a covalent bond.
In order to form a coordinate bond, the electron deficient species should have empty orbitals for the incoming electron pair. For example, in BF3 molecule, Boron (B) has an empty p orbital. Since the electron configuration of B does not obey the octet rule, it forms a coordinate bond with an electron-rich species such as NH3. There, the nitrogen atom has a lone electron pair that can be donated to the B atom of BF3. After the formation of this coordinate bond, all the bonds in the whole molecule looks similar.
Figure 2: Coordinate Bond between NH3 and BF3
Metals ions can form coordinate bonds with electron-rich species that are called ligands. Since metal ions are positively charged atoms, ligands can donate electron pairs to the metal atom. Since most of the metal atoms have empty d orbitals, the incoming electron pairs can be incorporated in those empty d orbitals. These metal-ligand complexes are called coordination complexes.
Similarities Between Covalent and Coordinate Bond
- After the formation of covalent and coordinate bonds, both types of bonds look the same.
- Both types of bonds are composed of one electron pair per each bond.
- Both types of bonds cause the attachment of two atoms together.
Difference Between Covalent and Coordinate Bond
Definition
Covalent Bond: A covalent bond is a type of chemical bond that is formed when two atoms share their unpaired electrons with each other.
Coordinate Bond: A coordinate bond is a type of chemical bond that is formed due to the donation of a lone electron pair by one atom to another atom.
Electron Donation
Covalent Bond: Two atoms donate an equal number of electrons for the bond formation.
Coordinate Bond: Only one atom donates a pair of electrons for the bond formation.
Presence of Unpaired Electrons
Covalent Bond: There should be unpaired electrons in order to form a covalent bond.
Coordinate Bond: There should be no unpaired electrons in order to form a coordinate bond.
Presence of Empty Orbitals
Covalent Bond: In order to form a covalent bond, empty orbitals are not required.
Coordinate Bond: Empty orbitals should be present in the electron deficient species in order to form coordinate bonds.
Presence of Lone Pair
Covalent Bond: In order to form a covalent bond, lone electron pairs are not required.
Coordinate Bond: In order to form a coordinate bond, at least one lone electron pair should be present in one of the two atoms.
Polarity of the Bond
Covalent Bond: Covalent bonds can be either polar or nonpolar according to the difference in the electronegativities of two atoms.
Coordinate Bond: Coordinate bonds are polar bonds.
Conclusion
Both covalent bond and coordinate bond are types of chemical bonds. They are helpful in holding atoms together in order to form compounds. After the formation of these bonds, both covalent bond and coordinate bond appear to be identical. But they are not the same. There is a distinct difference between covalent and coordinate bond; in a covalent bond, both atoms are involved in the formation of bond whereas, in coordination bond, only one atom is involved in the formation of the bond.
References:
1. “Ionic and Covalent Bonds.” Chemistry LibreTexts. Libretexts, 03 Mar. 2017. Web. Available here. 10 Aug. 2017.
2. “What is a dative covalent bond?” MyTutor. N.p., n.d. Web. Available here. 10 Aug. 2017.
Image Courtesy:
“Figure 02 01 08” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia
“NH3-BF3-adduct-bond-lengthening-2D” By Ben Mills – Own work (Public Domain) via Commons Wikimedia
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