General Chemistry
Intermolecular forces are electrostatic interactions between molecules and can be classified into three main types: London dispersion forces, dipole-dipole Interactions, and hydrogen bonds. London dispersion forces are a type of Van der Waals interaction caused by random fluctuations in electron density, creating temporary dipoles. These forces are experienced by all atoms and molecules and are stronger in larger atoms and molecules. However, they are the weakest of the intermolecular forces.
Dipole-dipole Interactions occur between molecules with permanent dipoles, which form when atoms of differing electronegativity cause electrons to spend more time around the electronegative atom. These interactions are stronger than London dispersion forces, but weaker than hydrogen bonds. Hydrogen bonds are the strongest of the intermolecular forces and form between an electronegative atom in one molecule (oxygen, nitrogen or fluorine) and a hydrogen atom covalently bonded to another electronegative atom in a different molecule. Compounds that are capable of forming hydrogen bonds have significantly higher boiling points, melting points, and solubility compared to those that do not. These bonds also contribute to a compound's stability, especially in the tertiary structure of proteins.
Lesson Outline
<ul> <li>Introducing Intermolecular Forces <ul> <li>Comparison between intermolecular forces and intramolecular forces</li> <li>Three important intermolecular forces: London dispersion forces, dipole-dipole interactions, and hydrogen bonds</li> </ul> </li> <li>London Dispersion Forces <ul> <li>Caused by random fluctuations in electron density</li> <li>Temporary dipoles form due to uneven electron distribution</li> <li>Stronger in larger atoms and molecules, weaker in smaller atoms and molecules</li> <li>Experienced by all atoms and molecules, even non-polar ones</li> <li>Weakest of the intermolecular forces</li> </ul> </li> <li>Dipole-Dipole Interactions <ul> <li>Only occur in polar molecules</li> <li>Formed due to permanent dipoles in polar molecules</li> <li>Attractive force between partially positive end of one polar molecule and partially negative end of another polar molecule</li> <li>Stronger than London dispersion forces, but weaker than hydrogen bonds</li> </ul> </li> <li>Hydrogen Bonds <ul> <li>Special kind of dipole-dipole interaction</li> <li>Occurs between an electronegative atom (O, N, F) and a hydrogen covalently bonded to an electronegative atom in a different molecule</li> <li>Hydrogen becomes partially positive, and the electronegative atom becomes partially negative</li> <li>Compounds with hydrogen bonds have higher boiling and melting points</li> <li>Increased solubility in water and contribution to stability</li> <li>Strongest type of intermolecular force</li> </ul> </li> </ul>
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FAQs
London dispersion forces are weak intermolecular forces that occur between temporary dipoles due to the random motion of electrons. These forces are present between all types of molecules, polar or nonpolar. Dipole-dipole interactions are stronger intermolecular forces occurring between molecules with permanent dipoles, such as polar molecules. Hydrogen bonds are a specific type of strong dipole-dipole interaction that occurs between a hydrogen atom bonded to a highly electronegative atom (usually nitrogen, oxygen, or fluorine) and another highly electronegative atom in a neighboring molecule.
Intermolecular forces, such as London dispersion forces, dipole-dipole Interactions, and hydrogen bonds, impact the boiling points of substances. A higher boiling point is indicative of stronger intermolecular forces present, requiring more energy to break these forces and change the substance from liquid to gas. As such, substances with hydrogen bonding typically have the highest boiling points, followed by those with dipole-dipole interactions and then those with London dispersion forces.
Intermolecular forces are forces that occur between different molecules, such as London dispersion forces, dipole-dipole interactions, and hydrogen bonds. These forces are responsible for the physical properties of a substance, like boiling point and melting point. Intramolecular forces, on the other hand, are forces occurring within a single molecule, such as covalent and ionic bonds. Intramolecular forces are generally much stronger than intermolecular forces and dictate a molecule's structure and chemical properties.
The strength of London dispersion forces between molecules is influenced by the size of the molecules and their corresponding electron cloud. Larger molecules with more electrons generally experience stronger London dispersion forces as their electron cloud is more easily distorted, leading to larger temporary dipoles. Additionally, molecular shape also affects the strength of these forces. Molecules with an elongated shape have a larger surface area, increasing the chances of experiencing stronger London dispersion forces when compared to more compact or spherical molecules.
