Intermolecular Forces
... as capillary action, which is characterized by two terms. In the case of H2O are the attractive forces between water molecules and a solid surface area is known as adhesive forces. This phenomenon is evidenced by the presence of an upward curvature known as a meniscus when water in measured using glass vessel. The reason for this occurrence is as a result of the adhesive forces being stronger than the cohesive ones. In opposite case of cohesive forces, during which the intermolecular forces tend to hold the liquid particles together, as in the case of mercury (Hg), a negative and downward curvature is seen. As final example, the viscosity, or the measure of a fluid’s resistance to flow, is likewise dependent upon intermolecular forces. The weaker the cohesive forces, the easier it is for the fluid’s particles to move past each other. Conversely, the stronger the cohesive forces, the more difficult it is for the particles to slide past each other. If a liquid is composed of long, chain-like molecules, the more viscous that liquid becomes as a result of the intermolecular forces acting upon their chain-like lengths. However, once H2O is in its solid state, the attractions of the intermolecular forces are strong enough to overpower the kinetic energy of the particles. This prevents the molecules from free-range movement, but allows them to vibrate about their positions. Intermolecular forces also affect the rigidity of solids. Generally, the more rigid a crystal is, then the stronger the molecular forces are acting on it. Based upon the dominant intermolecular force, solids can be classified to have one of four types of crystalline structures, two of which relate to intermolecular forces. The first type being atomic and molecular solids, when they are independent atoms and molecules and held together by intermolecular forces, their crystals tend to be soft, have low melting points, and are poor conductors of heat and electrical current. The other type, covalent-network solids, when covalently bonded, the crystals are hard, though most are poor conductors of heat and electrical current. In the case of graphite, its two-dimensional bonding pattern brings about layers that are held together by dispersion forces, and conducts electrical current along its planes well. Although, intermolecular forces the root of some changes in physical properties, it should be noted that these forces can be sub-divided into various groups, who affect a particular kind of molecule or ion. For example, one of the strongest types of intermolecular forces are called ion-ion forces, which consist of a cation, a negatively charges ion, and an anion, a positively charged ion. Though ions are typically characterized as intermolecular bonds, the particles can be considered as intermolecular forces once they have become disassociated, as in a solution. This particular type of force can be both attractive, as in the case of an anion and a cation interaction, but also can be repulsive, in as anion/anion and cation/cation interactions. However, the strength of these forces is dependent upon the ions themselves. For example, Na+ would have less intermolecular strength than Ca2+ because the calcium cation has a greater charge and greater molecular attractiveness to it as of a result of the extra electrons than the sodium cation has. Another type of intermolecular force is known as dipole-dipole forces, which are created by the attraction between the slightly negative and slightly positive sides of two particles. The partial charges are caused by a dipole, or the movement of electrons to one side of a polar molecule. During this occurrence, the negative region of one dipole will become attracted to the positive region of another dipole, causing them to align. The flaw with these interactions is that they tend to be weaker than those of ion-ion forces and only occur between other polar molecules. Under this heading type of intermolecular forces, one important type of dipole-dipole forces is characterized as, that being hydrogen bonding. This force is especially strong, occurring only when hydrogen atoms are covalently bonded to either a nitrogen, oxygen, or fluorine atom and is attracted to lone pair of the electronegative atoms of oxygen, fluorine, or nitrogen. Hydrogen bonding is one of the reasons that H2O has a number of unusual and interesting characteristics. For example, it is one of the reasons why H2O one of the largest values for surface tension and for its strong ability to prevent temperature changes. As a result of hydrogen bonding, it requires much energy (4.184 joules, to be exact) in order to raise the temperature of liquid water by one degree. A third type of intermolecular force is called an ion-dipole force, which occurs only during the mixture of ions and polar molecules. These forces tend to be generally stronger than dipole-dipole forces but not as strong as ion-ion forces. As with dipole forces, the strength of these particular forces is dependent upon the polarity of the molecule, as well as its size. Furthermore, molecules that are more closely compacted are one feature that attracts other molecules, resulting in the strength of these particular forces. The fourth intermolecular forces are known as either ion-induced dipoles or dipole-induced dipole forces. The significance of these particular forces is their capability to induce or force a normally nonpolar substance into becoming polar for a period of time. Under these circumstances, when either an ion or dipole approaches, all the available, meaning mobile and having low mass, electrons will move slightly in one direction while the nuclei will move into the opposite direction. In this case, the region in which the electrons are located will attract cations or the positive dipole region. The region housing...