Molecular forces are the fundamental concepts in chemistry that govern the behavior of molecules. Intramolecular forces are the forces that hold atoms together within a molecule, determining their structure and stability, whereas, intermolecular forces exist between molecules determining their physical properties.
Intramolecular forces include covalent bonds, where electrons are shared between atoms, and ionic bonds, where electrons are transferred between atoms. These forces are generally stronger than intermolecular forces and are responsible for the chemical properties of substances such as bond energies, bond lengths, and electronegativities.
Intermolecular forces, on the other hand, are the forces of attraction or repulsion between molecules. These forces arise due to the interactions between the charged or polarized regions of different molecules. These forces are relatively weaker than intramolecular forces and are responsible for determining the physical properties of substances such as boiling points, melting points, and solubilities.
Intra vs. Intermolecular Forces
| Intramolecular forces | Intermolecular forces |
| These forces are strong in nature | These forces are weak in nature |
| Intramolecular forces exists between atoms in a molecule | Intermolecular forces exists between molecules |
| They determine the chemical properties of a substance | They determine the physical properties of a substance |
| Relative strength is generally stronger | Relative strength is generally weaker |
| Their range of action is within a molecule | Their range of action is within different molecules |
| Intramolecular forces are essential for understanding molecular structure and chemical reactivity | Intermolecular forces are essential for explaining physical properties and intermolecular reaction |
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The types of intramolecular forces are:
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The types of intermolecular forces are:
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Intramolecular forces
Intramolecular forces also known as chemical forces are the forces that exist within a molecule. These forces are responsible for holding the atoms together within a molecule, determining its structure and stability. Intramolecular forces are typically much stronger than intermolecular forces.
These forces are sometimes named, bonding forces, and last longer in molecules. The parameters of physical change cannot affect such forces, however, chemical parameters such as reactivity, flammability, susceptibility to corrosion, etc of a substance are determined by such forces.
Intermolecular forces are usually liable for the stability of a molecule, therefore their interaction distance (bond length) is shorter.
The primary types of intramolecular forces are:
Ionic Bonds
When there is a complete transfer of electrons from one atom to another, resulting in the formation of ions, ionic bonds are formed. They are strong electrostatic attractions between positively and negatively charged ions.
Covalent Bonds
When atoms share electrons (mutually) to achieve a stable electron configuration, covalent bonds are formed. They are strong and can vary in strength depending on factors such as bond length and bond polarity.
Coordinate (Dative) Bonds
Dative bonds occur when one atom donates a pair of electrons to another atom. The atom accepting the electrons is known as Lewis acid, while the atom donating the electrons is called a Lewis base.
Metallic Bonds
Metallic bonds are found in metals and result from the delocalization of electrons throughout a metal lattice. This creates a sea of electrons that holds the metal atoms together.
Read more about; Conduction by Metals: Why do Metals Conduct electricity?
Importance of Intramolecular forces
Intramolecular forces play a crucial role in determining the chemical properties of substances, such as their reactivity, polarity, and shape. They are essential for understanding and predicting the behavior of molecules in chemical reactions.
Intermolecular forces
Intermolecular forces refer to the forces of attraction or repulsion that occur between molecules unlike intramolecular forces, which exist within a molecule. These forces are generally weaker than intramolecular forces.
These are sometimes named nonbonding forces and usually last for lesser time periods in molecules. The parameters of physical change such as melting points, boiling points, and physical states such as solid, liquid, or gas are determined by such forces.
Intramolecular forces are usually liable for the bulk properties of matter. Moreover, their interaction distance (bond length) is longer than the other forces.
The primary types of intermolecular forces are:
Dipole-Dipole Interactions
These forces arise between molecules with permanent dipoles. The positive end of one polar molecule is attracted to the negative end of another polar molecule, resulting in dipole-dipole interactions.
Ion-Dipole Interactions
Ion-dipole interactions occur when an ion interacts with a polar molecule. The charged ion is attracted to the opposite partial charges on the polar molecule.
Ion-Induced dipole Interactions
Ion-induced dipole interactions exist when an ion (charged particle) interacts with a non-polar molecule, inducing a temporary dipole in the non-polar molecule. These forces play a crucial role in the interactions between ions and non-polar substances.
Van der Waals Forces
These are weak forces that arise due to temporary fluctuations in electron distribution, creating temporary dipoles. Van der Waals forces consist of London dispersion forces, which occur in all molecules, and dipole-induced dipole interactions.
Hydrogen Bonding
Hydrogen bonding is a specific type of intermolecular force that occurs when a hydrogen atom is bonded to a highly electronegative atom (such as oxygen, nitrogen, or fluorine) and is attracted to another electronegative atom in a nearby molecule.
Importance of Intermolecular forces
Intermolecular forces play a significant role in determining the physical properties of substances, including boiling points, melting points, vapor pressure, and their solubilities. These forces are responsible for the cohesion between molecules and affect the behavior of substances in condensed phases (such as liquids and solids).
Read more about; Solid, Liquid, and Gases: A Comparison
Key Takeaway(s)
Concepts Berg
What is the difference between intermolecular and intramolecular forces?
Intramolecular forces are the forces that hold atoms together within a molecule. Intermolecular forces are forces that exist between molecules.
Are intermolecular forces stronger than intramolecular forces?
Generally, intramolecular forces are stronger than intermolecular forces. Whereas, in intermolecular forces, ion-dipole is the strongest, followed by hydrogen bonding, then dipole-dipole, and then London dispersion.
What are three examples of intermolecular bonds?
Examples of intermolecular forces include the London dispersion force, dipole-dipole interaction, ion-dipole interaction, and van der Waals forces.
How do intermolecular forces affect the boiling point of a substance?
Intermolecular forces influence boiling points. Stronger forces, like hydrogen bonding, require more energy to break, leading to higher boiling points for substances with these interactions.
What is the difference between dipole-dipole interactions and hydrogen bonding?
Dipole-dipole interactions occur between polar molecules, where permanent dipoles attract each other. Hydrogen bonding on the other hand, is a specific, stronger type of dipole-dipole interaction that involves hydrogen bonded to a highly electronegative atom (N, O, or F).
What is the strongest intermolecular force?
Hydrogen bonding is the strongest intermolecular force. It occurs between a hydrogen atom bonded to an electronegative atom (N, O, or F) and a lone pair on another electronegative atom.
How do intermolecular forces affect the solubility of a substance?
Intermolecular forces affect the solubility of a substance because the stronger the forces between a compound’s molecules, the harder it will be to break it apart and dissolve.
What are some examples of intermolecular forces in everyday life?
Some examples of intermolecular forces in everyday life include:
- Water forms droplets due to hydrogen bonding.
- Sugar dissolves in water (polar-polar interactions).
- Oil and water separate due to their differing polarities.
- Evaporation of liquids by overcoming intermolecular forces.
- Geckos stick to surfaces through van der Waals forces.
References
- Tutortube for Spring 2020 (University of North Texas)
