Intermolecular Forces Overview & Examples

Joanna Tatomir, Nathan Crawford
  • Author
    Joanna Tatomir

    Joanna holds a PhD in Biology from the University of Michigan and is currently working towards a degree in Veterinary Medicine at Michigan State University. She has taught a combination of ESL and STEM courses to secondary and university students.

  • Instructor
    Nathan Crawford

    Nathan, a PhD chemist, has taught chemistry and physical science courses.

Explore intermolecular forces. Learn the definition of intermolecular force and understand its different types. Discover intermolecular forces examples in real life. Updated: 02/14/2022

Table of Contents


Intermolecular Forces Definition

In chemistry, atoms are held together by a variety of bonds. The two major bonds connecting atoms together include covalent and ionic bonding. Covalent bonding occurs when atoms share electrons with one another. By contrast, ionic bonding represents the attractive forces occurring between oppositely charged ions. These bonds represent types of intramolecular bonds.

When larger molecules are formed by these types of bonds, a variety of intermolecular forces can hold atoms together both within and between larger chemical structures. Individually these intermolecular forces tend to be weak, but the combination of many intermolecular forces within larger molecules can provide both strength and structure to complex molecules. In DNA, for example, the double helix structure is formed in part by the intermolecular forces occurring between the different components of DNA.

Intermolecular forces largely arise due to the manner in which electrons are shared within the covalent bonds of different molecules. Depending on how the electrons are shared between atoms, partial charges can form on one or more atoms, enabling different intermolecular forces to develop. These intermolecular forces are responsible in part for the changes in state between gases, liquids, and solids.

In this lesson, the different types of intermolecular forces will be presented, along with examples for each type of force.

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Intermolecular Forces in Molecules

As mentioned earlier in this lesson, certain types of intermolecular forces develop when there are differences in the sharing of electrons within the covalent bonds between atoms. When this happens, there is the potential for partial charges to occur when the electrons have a greater attraction to one of the atoms in a covalent bond. This typically occurs when an atom possesses strong electronegativity, or the ability to attract electrons to itself.

When atoms with low electronegativity, such as carbon and hydrogen, are involved in a covalent bond, both atoms share the electrons equally. This results in the production of a non-polar molecule. By contrast, when an atom with high electronegativity forms a covalent bond with a low electronegative element, such as between oxygen and carbon, the electrons are shared unequally between the two atoms. This creates a polar bond between the two atoms.

In some instances, when a polar bond forms between two atoms, a partial positive and a partial negative charge can develop. The partial positive charge is found on the more electronegative atom while the partial negative charge forms on the less electronegative atom. The presence of a partial positive and partial negative charge in a molecule is referred to as a dipole. As will be seen later in this lesson, both polar bonds and dipoles play important roles in the formation of intermolecular forces.

A diagram showing the formation of a dipole moment with partial negative and positive charges.

intermolecular forces definition chemistry: dipole moment

Types of Intermolecular Forces

There are three main types of intermolecular forces studied by chemists. These include ion-dipole forces, dipole-dipole forces, and London, or London dispersion, forces. These three types of intermolecular forces will be further discussed in the following sections.

Ion-Dipole Forces

Much like dipole-dipole forces, which will be discussed in more detail in the following section, ion-dipole forces form due to the attractive forces between an ion and a molecule with a dipole moment, or partial charge. An ion represents any atom that possesses either a net positive or a negative charge. A positive ion is referred to as a cation, while a negative ion is known as an anion. With ion-dipole interactions, a cation is attracted to the partial negative charge of another molecule, while an anion is attracted to the partial positive charge of a second molecule. Mixing table salt (NaCl) or a calcium ion ({eq}Ca^{2+} {/eq}) with water represents one example of an ion-dipole intermolecular force.

Dipole-Dipole Forces

As described earlier in this lesson, dipoles form when different atoms in a molecule possess partial positive and partial negative charges. When these dipoles form, the partial negative charge in one molecule can attract the partial positive charge from a second molecule, much like the ionic bonds formed between ions. The presence of these partial charges causes the negative dipole to line up next to the positive dipole, thus forming a dipole-dipole interaction.

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Frequently Asked Questions

What is an example of intermolecular forces in real life?

DNA represents the double helix structure responsible for the transmission of genetic material in living organisms. The double helix structure is formed by intermolecular forces such as hydrogen bonding between the oxygen and hydrogen atoms of adjacent proteins in DNA.

What is the definition of intermolecular force?

An intermolecular force represents a type of interaction that occurs between molecules. Intermolecular forces arise due to the presence of partial positive and negative charges when electrons are shared unequally in a covalent bond.

What does intermolecular mean in science?

Intermolecular refers to the interactions that occur between molecules. These forces form when partial positive and partial negative charges form in a molecule.

What are the types of intermolecular forces?

There are three different types of intermolecular forces. These intermolecular forces include: ion-dipole interactions, dipole-dipole forces, and London dispersion forces.

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