Difference Between Covalent and Hydrogen Bonds

Main Difference – Covalent vs Hydrogen Bonds

Chemical bonds are linkages that occur between atoms. These chemical bonds are helpful in holding atoms together in order to form molecules and complex compounds. Chemical bonds are formed either due to the exchange of electrons between atoms or due to the attraction between atoms, ions or molecules. Covalent bond and hydrogen bond are two types of chemical bonds that can be found among covalent compounds. A covalent bond is formed due to sharing of electrons between atoms. A hydrogen bond is formed due to the attraction between two atoms of two different molecules. The main difference between covalent and hydrogen bonds is that covalent bonds are intramolecular attractions whereas hydrogen bonds are intermolecular attractions.

Key Areas Covered

1. What are Covalent Bonds
      – Definition, Formation of Bond with Examples
2. What are Hydrogen Bonds
      – Definition, Formation of Bond with Examples
3. What are the Similarities Between Covalent and Hydrogen Bonds
      – Outline of Common Features
4. What is the Difference Between Covalent and Hydrogen Bonds
      – Comparison of Key Differences

Key Terms: Atoms, Attraction Force, Covalent Bond, Hydrogen Bond, Intermolecular Attractions, Intramolecular Attractions, Ions, Molecules

Difference Between Covalent and Hydrogen Bonds - Comparison Summary

What are Covalent Bonds

Covalent bonds are chemical bonds that are formed due to the sharing of electrons between atoms. Therefore, it is called an intermolecular attraction force. The bond is formed between two atoms that contain unpaired electrons. These unpaired electrons are paired with the unpaired electrons of another atom to form a covalent bond.

Atoms can have covalent bonds as single bonds, double bonds or triple bonds between atoms. One covalent bond comprises one bond electron pair; when one unpaired electron is coupled with another unpaired electron of a different atom, a covalent bond is formed and these two electrons are called bond electron pair or bond pair. Therefore, in a double bond, 4 electrons are shared between two atoms because there are 2 covalent bonds having two bond pairs.

The main purpose of formation of a covalent bond is to fill the outermost orbitals of atoms in order to get stabilized. Covalent bonding is found among nonmetals and metalloids. Covalent bonds are very strong attractions and the covalent bond strength ranges from 100 to 1100 kJ/mol.

Difference Between Covalent and Hydrogen Bonds

Figure 1: Dot-cross Structure of Hydrogen Fluoride

The above image shows the covalent bond between hydrogen (H) atom and fluorine (F) atom. Here, the cross mark indicates the unpaired electron in the hydrogen atom and dot marks show the electrons in the outermost orbital of fluorine.

There are two main types of covalent bonds: polar covalent bonds and nonpolar covalent bonds. These two bonds are named according to the polarity of the covalent bond. The polarity of the bond depends on the electronegativity values of the two atoms that contribute to the covalent bond. If the difference between these electronegativity values is less than 0.4, it is a nonpolar covalent bond. If that value is between 0.4 and1.7, it is a polar covalent bond. In the above example, the electronegativity of hydrogen is 2.2 and electronegativity of fluorine, is 4.0. Therefore the difference is (4.0-2.2) = 1.8. Therefore it is a highly polar covalent bond.

What are Hydrogen Bonds

Hydrogen bonds are attraction forces that occur between two atoms of two different molecules. Therefore, it is an intramolecular attraction. It is a weak attraction force. But when compared to other types of intramolecular forces such as polar-polar interactions, nonpolar-nonpolar interactions like Vander Waal forces, the hydrogen bond is stronger.

Hydrogen bonding occurs between polar covalent compounds. These compounds (or molecules) are composed of polar covalent bonds. A polar covalent bond arises due to the difference in the electronegativity values of the atoms that are in the covalent bond. If this difference is high, the highly electronegative atom tends to attract the bond electrons towards itself. This creates a dipole moment where this highly electronegative atom gets a partial negative charge whereas the other atom gets a partial positive charge. Then the bond becomes a polar covalent bond. When this molecule meets another molecule that has a dipole moment like this, the negative and positive charges tend to attract each other. This attraction force is called a hydrogen bond.

Hydrogen bonding occurs between highly electronegative atoms and less electronegative atoms. Hydrogen bonds exist when we have O, N and F in one molecule and positive charged H in the other molecule. This is because F, N and O are the most electronegative atoms that are capable of forming hydrogen bonds. The strength of a hydrogen bond may vary from 5 to 50 kJ/mol. The strongest hydrogen bond occurs between HF atoms.

Main Difference - Covalent vs Hydrogen Bonds

Figure 2: Hydrogen Bonds between Water Molecules

Water is the most common example for a compound having hydrogen bonds. Here, the oxygen atom of one water molecule can attract a hydrogen atom of another molecule due to the charge separation in that molecule.

Similarities Between Covalent and Hydrogen Bonds

  • Covalent and hydrogen bonds are types of chemical bonds.
  • Both types of bonds occur between two atoms.
  • Both types of bonds act as a glue between two atoms.

Difference Between Covalent and Hydrogen Bonds

Definition

Covalent Bonds: Covalent bonds are chemical bonds that are formed due to the sharing of electrons between atoms.

Hydrogen Bonds: Hydrogen bonds are attraction forces that occur between two atoms of two different molecules.

Nature of Bond

Covalent Bonds: Covalent bonds are intermolecular chemical bonds.

Hydrogen Bonds: Hydrogen bonds are intramolecular chemical bonds.

Chemical Species

Covalent Bonds:  Covalent bonds are formed between two atoms.

Hydrogen Bonds: Hydrogen bonds are formed between two atoms of two different molecules.

Bond Strength

Covalent Bonds: The bond strength of covalent bond may vary from 100 to 1100 kJ/mol.  

Hydrogen Bonds: The bond strength of hydrogen bond may vary from 5 to 50 kJ/mol.

Conclusion

Both covalent bonds and hydrogen bonds are chemical bonds. Covalent bonds are stronger than hydrogen bonds. This is because a covalent bond is formed due to sharing of electrons between two atoms whereas a hydrogen bond is formed due to the attraction between two molecules. The main difference between covalent and hydrogen bonds is that covalent bonds are intramolecular attractions whereas hydrogen bonds are intermolecular attractions.

References:

1. Libretexts. “Hydrogen Bonding.” Chemistry LibreTexts, Available here.  17 Jan. 2017. Accessed 16 Aug. 2017.
2. “Covalent bonding.” BBC, Available here. Accessed 16 Aug. 2017.

Image Courtesy:

1. “Hydrogen-fluoride-2D-dot-cross” By Benjah-bmm27 – Own work (Public Domain) via Commons Wikimedia
2. “Hydrogen-bonding-in-water-2D” (Public Domain) via Commons Wikimedia

About the Author: Madhusha

Madhusha is a BSc (Hons) graduate in the field of Biological Sciences and is currently pursuing for her Masters in Industrial and Environmental Chemistry. Her interest areas for writing and research include Biochemistry and Environmental Chemistry.

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