What is the Difference Between Van Der Waals and Hydrogen Bonds

The forces that attract molecules together are known as intermolecular forces. However, they are weaker compared to chemical bonds inside molecules. Van der Waals forces and hydrogen bonds are types of intermolecular forces that occur between molecules. In fact, hydrogen bonds are a special type of Van Der Waals bonds.

What is the difference between Van Der Waals and hydrogen bonds? Hydrogen bonds are stronger and more specific than van der Waals forces.

Key Areas Covered

1. What are Van Der Waals Bonds
      – Definition, Features
2. What are Hydrogen Bonds
      – Definition, Features 
3. Similarities Between Van Der Waals and Hydrogen Bonds
      – Outline of Common Features
4. Difference Between Van Der Waals and Hydrogen Bonds
      – Comparison of Key Differences
5. FAQ: Van Der Waals and Hydrogen Bonds
      – Answers to Frequently Asked Questions

Key Terms

Van Der Waals Bonds, Hydrogen Bonds

What are Van Der Waals Bonds

Van Der Waals forces /bonds are a type of intermolecular forces that bind molecules together. These forces are found in solids, liquids, and gases. There are three main types of such forces.

Types of Van Der Waals Bonds

London Dispersion Forces

• These are the weakest type of forces that exist between molecules. They exist regardless of the polarity of the molecule. They occur due to temporary fluctuations in electron density within a molecule.

Dipole-Dipole Forces

• Polar molecules having permanent dipoles have dipole-dipole type of interaction forces among them. The positive end of one molecule is attracted to the negative end here. This creates a weak electrostatic attraction.

Ion-Dipole Forces

• This type of force exists between ions and polar molecules. The ion’s charge attracts the oppositely charged end of the polar molecule. This creates a strong electrostatic attraction.

Van Der Waals forces determine the properties of substances, such as boiling points, melting points, and solubility. Stronger Van der Waals forces, for instance, cause compounds to have higher boiling points since it takes more energy to overcome them and cause the liquid to evaporate. Similarly, because they are more attracted to one another than to water molecules, compounds with stronger Van der Waals forces are less soluble in water. These types of bonds are weaker than covalent and ionic bonds.

What are Hydrogen Bonds

When a hydrogen atom is covalently bonded to a highly electronegative atom, the electronegative atom attracts the electron density away from the hydrogen atom. This creates a partial positive charge on the hydrogen and a partial negative charge on the electronegative atom. Due to its polarity, the hydrogen atom can weakly form an electrostatic attraction with a single electron pair on an electronegative atom that is either adjacent or a part of the same molecule. This attraction force thus formed is called the hydrogen bond. Hydrogen bonds can be found in water, proteins, DNA, and enzymes.

There are certain characteristics of hydrogen bonds.

• Strength – In comparison to covalent and ionic bonding, hydrogen bonds are comparatively weak. Their bond energies are usually between 5 and 40 kJ/mol.
• Length – Though shorter than van der Waals interactions, hydrogen bonds are usually longer than covalent bonds.
• Directionality – With the hydrogen atom pointing straight toward the lone pair on the electronegative atom, hydrogen bonds are extremely directed.
• Importance – Numerous biological and chemical processes, such as protein structure, DNA base pairing, and enzyme catalysis, depend on hydrogen bonding.

Similarities Between Van Der Waals and Hydrogen Bonds

• Both are considered weak attractions between molecules.
• They occur between molecules, not within them.
• Both contribute to the physical properties of substances, such as boiling point, melting point, and viscosity.

Difference Between Van Der Waals and Hydrogen Bonds

Definition 

• Van der Waals forces are weak intermolecular attractions between molecules due to temporary dipoles. Hydrogen bonds, on the other hand, are stronger intermolecular bonds occurring when hydrogen is covalently bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine.

Strength

• Hydrogen bonds are stronger than van der Waals forces.

Specificity

• Hydrogen bonds are more specific than van der Waals forces.

Direction

• Hydrogen bonds are more directional than van der Waals forces.

Common In

• Hydrogen bonding is more common in molecules containing O, N, or F atoms, while Van der Waals forces are more common in all types of molecules, especially in nonpolar molecules.

Conclusion

Intermolecular forces are the attractive forces between molecules. Hydrogen bonds and Van der Waals bonds are two such types of intermolecular forces. Van der Waals forces include weaker interactions like London dispersion forces and dipole-dipole interactions, while hydrogen bonds are a stronger type of dipole-dipole interaction specific to certain molecules. This is the basic difference between Van Der Waals and hydrogen bonds.

FAQ: Van Der Waals and Hydrogen Bonds

1. Which attraction is stronger, the hydrogen bond or the van der Waals forces?

Hydrogen bonds are stronger than van der Waals forces. Hydrogen bonds involve a shared electron pair between a hydrogen atom and a highly electronegative atom (usually oxygen, nitrogen, or fluorine), while van der Waals forces are temporary attractions between molecules caused by fluctuations in electron density.

2. Is Van der Waals the weakest bond?

No, Van der Waals forces are not the weakest bond. They’re actually the weakest type of intermolecular force. Covalent bonds, ionic bonds, and metallic bonds are all stronger than Van der Waals forces.

3. Why is a hydrogen bond stronger?

Hydrogen bonds are stronger than other dipole-dipole interactions due to the high electronegativity difference between hydrogen and the electronegative atoms it bonds with (usually oxygen, nitrogen, or fluorine). This creates a strong partial positive charge on the hydrogen atom and a strong partial negative charge on the electronegative atom, leading to a strong electrostatic attraction.

4. What is an example of a van der Waals bond?

A van der Waals bond is a weak intermolecular force that occurs between all molecules. An example of a van der Waals bond is the attraction between two helium atoms in a helium gas.

Reference:

1. “Hydrogen Bonding.” Encyclopedia Britannica.
2. “Van Der Waals Bond.” Science Direct.

Image Courtesy:

1. “Vectorial representation of the interaction of two dipolar molecules” By Cnrowley – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “3D model hydrogen bonds in water” (CC0) via Picryl