Intramolecular Forces

intramolecular forces

Core Concepts

An intramolecular force is a force that holds atoms together to form a molecule. There are three main types of these forces: covalent, ionic, and metallic, and each results in different chemical properties. Intramolecular forces shouldn’t be confused with intermolecular forces, which are forces caused by interactions between separate whole molecules. 

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What are Intramolecular Forces?

Intramolecular forces are the forces that hold atoms together to form molecules. There are several different ways that atoms can interact with each other, which results in different types of forces between them. There are three main types, which are covalent, ionic, and metallic. Each force will hold the molecule together in different ways, giving substances with various corresponding properties.

Intramolecular vs. Intermolecular Forces

Despite being a similar sounding word, intramolecular forces are different than intermolecular forces. While intramolecular forces are between atoms inside a molecule, intermolecular forces are interactions between separate whole molecules, such as the hydrogen bonding that occurs when multiple water molecules are near each other. The many types of intermolecular forces also create varying properties in substances, but the type of intermolecular force between molecules is heavily influenced by the charge or polarity of a molecule, which comes from its intramolecular force. In contrast to the above example, an intramolecular force in a water molecule would be the bond that keeps the two H atoms attached to the O, and it’s because of the polarity of the covalent bond that hydrogen bonding occurs the way it does, as shown below. For a more in-depth analogy about how these forces are related, see here

intermolecular vs intramolecular forces

Types of Intramolecular Forces

As previously stated, there are several types of intramolecular forces. Each type creates different types of molecules, and therefore different properties of the substances. 

Covalent bonds

Covalent bonds are the type of force in which two atoms share an electron pair. These occur between two atoms that are seeking an octet (learn more about octets and the octet rule here!), where the atoms will simultaneously keep the same electron pair in their respective valence shells, bonding them to each other. The diagram shows how two atoms share an electron pair, resulting in a bond. This can happen to create either a polar bond or a nonpolar bond, depending on each atom’s electronegativity (affinity to pull electrons close to them, learn about electronegativity in more detail here).

covalent bonds

Polar Covalent Bonds

When a covalent bond occurs between two atoms with different electronegativities, the bond is polar. This is because one of the atoms will have a stronger affinity for the electrons than the other, and will pull them closer to itself than the other atom. This creates a dipole, giving one atom a partial negative charge while the other has a partial positive charge. In some cases, dipoles can be so strong that they interact with surrounding ions or other polar molecules. These would be examples of intermolecular forces, which were discussed earlier. 

polar covalent bonds

Nonpolar Covalent Bonds

Conversely, covalent bonds between atoms of the same electronegativity produce nonpolar covalent bonds. A bond is nonpolar if neither atom pulls on the electrons stronger than the other, and they end up perfectly shared between them. Oftentimes, this means two of the same atom covalently bonding to one another where the electronegativities are exactly equal, however there are also nonpolar covalent bonds between different atoms with highly similar electronegativities, such as between carbon and hydrogen. 

nonpolar covalent bonds

Ionic Bonds

Unlike covalent bonds, ionic bonds do not share electrons. Instead, an ionic bond occurs when one atom donates an electron to another one nearby. This happens when a metal and a nonmetal both seek an octet. The metal will completely transfer one of its valence electrons to the nearby nonmetal, producing oppositely charged ions. These now stable ions then attract each other because of the opposing charges, creating an ionic force between them.  

ionic bond intramolecular forces

Metallic Bonds

Metallic bonds are a bit different than the other two types. They only occur inside metals, and because metals tend to have a loose hold on their electrons, the forces between metal atoms are unique. The nuclei of metal atoms remain in one place, while all electrons can move around the nuclei, referred to as the “sea of electrons”. Because of this, metals are incredibly conductive of electricity, since electrons and therefore charges are easily able to move around and be transferred throughout it.

metallic bond intramolecular forces

The intramolecular forces and interactions between molecules that create them are heavily involved with other topics of chemistry. Which type of intramolecular force a molecule has goes on to effect how it interacts with other molecules around it, and thus the properties of any substance made up of it. Because of this, understanding intramolecular forces is key to having a deeper understanding of how many aspects of chemistry works.