Intermolecular Forces of Attraction PDF

Intermolecular forces of attraction influence the properties of solids and liquids. Intermolecular Forces of Attraction pertain to forces that hold individual particles such as atoms, molecules or ions together. Ions...

Intermolecular forces of attraction influence the properties of solids and liquids. Intermolecular Forces of Attraction pertain to forces that hold individual particles such as atoms, molecules or ions together. Ions are charged particles that form when atoms or molecules gain or lose electrons. Cations: Positively charged ions, formed when an atom or molecule loses one or more electrons. Anions: Negatively charged ions, formed when an atom or molecule gains one or more electrons.  The intermolecular forces of attraction influence the resulting properties of solids, liquids and gases. In solids, for example, the intermolecular forces of attraction directly affect its melting point and heat of fusion. The melting point is the temperature at which a solid turns into a liquid. At this temperature, the substance reaches a point where the kinetic energy of the particles is sufficient to overcome the intermolecular forces that hold the solid together.  The heat of fusion (also called the enthalpy of fusion) is the amount of heat energy required to convert a unit mass of a solid into a liquid at its melting point, without changing the temperature. In other words, it’s the energy required to overcome the intermolecular forces that hold the particles in place in the solid state. A substance with stronger intermolecular forces requires more energy to break those bonds and transition into a liquid, meaning it has a higher heat of fusion. Stronger forces lead to a higher heat of fusion. Weaker forces lead to a lower heat of fusion. The intramolecular forces of attraction, on the other hand, are those responsible for interactions within a molecule, such as covalent and ionic bonds. An ionic bond forms when one atom loses electrons and another gains electrons, resulting in the formation of ions (charged particles). A covalent bond forms when two non-metal atoms share electrons in order to achieve a stable electron configuration, usually following the octet rule (eight electrons in the outermost shell, like the noble gases). For example, Helium (He), Neon (Ne), Argon (Ar)  Several types of intermolecular forces of attraction Note that the term Van der Waals forces named after the Dutch scientist Johannes Diderik van der Waals is sometimes used when referring to these types. 1. London dispersion force - named after the German- born physicist Fritz London, this is the weakest among the intermolecular forces. This dispersion force is caused by polarization or the distortion of the electron cloud brought about by the presence of a highly charged particle. In this case, the electron cloud of one atom is attracted to the positively charged nucleus of another atom.  The force that allows a lizard to climb walls or walk on ceilings without falling is called van der Waals forces, specifically a type known as adhesive van der Waals forces. Lizards, particularly geckos, have specialized toe pads that are covered with microscopic hair-like structures called setae. These setae increase the surface area for interaction with the surface of the wall. The tips of the setae are covered with even smaller structures called spatulae.  Here's how the process works: 1. The spatulae create a very large surface area in contact with the surface they are climbing. 2. These small structures interact with the surface using van der Waals forces (specifically London dispersion forces). 3. Although each individual force is weak, the cumulative effect of millions of these interactions provides enough adhesion to support the lizard’s weight, allowing it to stay attached to vertical or even upside-down surfaces. This remarkable ability is an example of molecular adhesion driven by van der Waals forces.  The London dispersion force occurs in all types of molecules, such as Carbon Dioxide, Hydrogen, Oxygen, Nitrogen and Halogens such as xenon or argon. London dispersion forces exist in all substances including inert gases.  2. Dipole-dipole Interaction - this is an intermolecular force of attraction that occurs between partially positive and partially negative ends. This interaction is observed in polar covalent molecules such as amino acids, wherein the electrons are shared both by oxygen and carbon atoms. Hydrogen Chloride A dipole refers to a separation of positive and negative charges within a molecule or a system. It occurs when there is a difference in electronegativity between two atoms in a covalent bond, resulting in an uneven distribution of electron density. This creates a region of partial positive charge (δ⁺) on one atom and a region of partial negative charge (δ⁻) on the other atom. (δ⁺) (δ⁻)  3. Ion-dipole interaction - this arises from the interaction between an ion and a polar molecule. If the molecule is an anion (negatively charged ion) it will be attracted to the partially positive end of the polar molecule; however, if the molecule is a cation (positively charged ion) it will be attracted to the partially negative end of the polar molecule. Example of Ion-Dipole Interaction: Dissolution of sodium chloride (NaCl) in water: When sodium chloride (NaCl) dissolves in water, it dissociates into sodium ions (Na⁺) and chloride ions (Cl⁻). These ions interact with water molecules, which are polar and have a dipole moment.  4. Hydrogen bond- is a special kind of dipole-dipole bond interaction, which is formed when hydrogen bonds with fluorine, oxygen or nitrogen. Hydrogen bonding is an important intermolecular force that affects the physical properties of molecules.