Hydrogen molecule dispersion forces among

Surface tension decreases as intermolecular forces decrease. You can t float a paper clip on benzene, for example, because the dispersion forces among the molecules composing benzene are significantly weaker than the hydrogen bonds among water molecules. The surface tension of benzene is only 28 mJ/m —just 40% that of water. 

There are three main types of intermolecular forces you need to be aware of hydrogen bonding, dipole-dipole interactions, and London dispersion forces. The first two only occur in polar molecules, whereas dispersion forces exist among all types of molecules. 

Intramolecular forces do not account for all attractions between particles. There are forces of attraction called intermolecular forces. The prefix inter-means "between" or "among." For example, an interview is a conversation between two people. Intermolecular forces can hold together identical particles, such as water molecules in a drop of water, or two different types of particles, such as carbon atoms in graphite and the cellulose particles in paper. The three intermolecular forces that will be discussed in this section are dispersion forces, dipole-dipole forces, and hydrogen bonds. Although some intermolecular forces are stronger than others, all intermolecular forces are weaker than intramolecular, or bonding, forces. 

The van der Waals radius determines the shortest distance over which intermolecu-iar forces operate it is aiways larger than the covalent radius. Intermolecular forces are much weaker than bonding (intramolecular) forces. Ion-dipole forces occur between ions and poiar molecules. Dipole-dipole forces occur between oppositely charged poles on polar molecules. Hydrogen bonding, a special type of dipole-dipole force, occurs when H bonded to N, O, or F is attracted to the lone pair of N, O, or F in another molecule. Electron clouds can be distorted (polarized) in an electric field. Dispersion (London) forces are instantaneous dipole-induced dipole forces that occur among all particles and increase with number of electrons (molar mass). Molecular shape determines the extent of contact between molecules and can be a factor in the strength of dispersion forces. 

Consider what happens when the two immiscible liquids, methanol whose P is 5.1 and hexane whose P is 0.1, are in contact with each other. The weak dispersion forces are present throughout hexane, whereas the much stronger interaction due to hydrogen-bonding among methanol molecules exist this is shown in the following ... 

All solids and liquids are held together by cohesive forces among molecules or atoms. Because our own bodies are a complex mixture of solids and liquids, even we are held together by these forces. If not for cohesive forces, all matter would be gaseous. The major cohesive forces that occur between molecules in order of increasing strength are the dispersion force, the dipole force, and the hydrogen bond. 

Crystals are usually categorized by the type of interactions operating among the atoms, molecules, or ions of the substance. These interactions include ionic, metallic, and covalent bonds as well as intermolecular forces such as hydrogen bonds, dipole-dipole forces, and London dispersion forces. 

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