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Introduction
Intermolecular forces are the forces that attract molecules together. They determine various bulk properties, including melting points, temperatures, boiling points, and solubilities (miscibilities) of substances. Compared to a low-boiling-point liquid, such as hexane (C6H14, b.p. 68.73 °C), a high-boiling-point liquid, such as water (H2O, b.p. 100 °C) exhibits stronger intermolecular forces. Ion–dipole forces, dipole-dipole interactions, and Van der Waals forces, including London dispersion forces, are among the types of intermolecular interactions. The electrostatic attraction between an ion and a dipole is known as ion-dipole forces. They’re common in solutions and play a key role in the dissolving of ionic compounds in water, such as KCl. The strength of ion-dipole interactions are related to i) the ion’s charge and ii) the magnitude of polar molecules’ dipole.Properties of intermolecular interactions
Weak interactions between particles are known as intermolecular (or interparticle) forces. As you progress from solid to liquid to gas, they decrease. Remember that in a gas, particles have the greatest degree of freedom of movement and intermolecular interactions are low or weak. The vapour pressure (the pressure of a vapour in equilibrium with its liquid) drops as the intermolecular attraction increases As the temperature rises, the boiling point (the temperature at which the vapour pressure equals the pressure imposed on the liquid’s surface) rises Surface tension (a liquid’s resistance to spreading out and increasing its surface area) rises Viscosity (a liquid’s resistance to flow) risesWhat effect do intermolecular forces have on matter states?
- The balance between the kinetic energy of individual particles (molecules or atoms) and intermolecular forces determines the state of a substance. When you apply more pressure to a substance, the molecules are forced closer together, which strengthens the intermolecular forces.
- The higher the intermolecular interactions between liquid particles, the more difficult it is for it to escape into the vapour phase, i.e., more energy is required to convert it from liquid to vapour phase, resulting in a higher boiling point.
- Stronger physical properties, such as higher melting or boiling temperatures, will come from stronger intermolecular forces, which necessitate breaking molecules apart. Because it is easier to evaporate a compound with greater vapour pressure, fewer intermolecular tensions result in higher vapour pressure.
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Melting and boiling points:
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Surface tension:
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Viscosity:
