Intermolecular Forces

Intermolecular forces are the electromagnetic force that occurs etween widely separated parts of a macro-molecule. These forces of cohesion Between cans similar molecules, Such as for example the surface tension, or the adhesion between unlike molecules, for example on capillarity. These forces, starting from the most powerful, consisting of: ionic interactions, bond hydrogen, dipole interaction (dipole), and Van der Waals force.

1. Hydrogen bond

In chemistry, hydrogen bonding is a type of intermolecular attractive force that occurs between two partial electric charges with opposite polarity. Although stronger than most of the intermolecular forces, hydrogen bonding is much weaker than covalent bonds and ionic bonds. In macromolecules such as proteins and nucleic acids, this bonding can occur between two parts of the molecule the same. and acts as a determinant of overall molecular shape important. Hydrogen bonding occurs when a molecule has an atomic N, O, or F.which have a lone pair (lone pair electrons). Hydrogen from other molecules will interact with the lone pair form a hydrogen bond with large bond varies from weak (1-2 kJ mol-1) to high (> 155 kJ mol-1).Hydrogen bond strength is influenced by differences in electronegativity between atoms in the molecule. The bigger the difference, the greater the hydrogen bonds are formed.Hydrogen bonds affect the boiling point of a compound. The more hydrogen bond, the higher the boiling point. However, specialized in water (H2O), there are two hydrogen bonds in each molecule. As a result the total number of hydrogen bonds is greater than the fluoride acid (HF), which should have the largest hydrogen bonding (because the highest electronegativity differences) so that the boiling point of water higher than the acid fluoride.

2. Style van der walls

Van der Waals force in chemistry refers to certain types of forces between molecules. This term originally refers to any type of forces between molecules, and it is still sometimes used in the sense that, but today more commonly refers to the forces arising from the polar ization of molecules into dipole. This includes forces that arise from permanent dipoles (Keesom forces), dipole rotation or free (Debye forces) as well as a shift in the distribution of awanel ektron (style London). The name of this style is taken from a Dutch chemist Johannes van der Waals forces, who first noted this type of style. Potential Lennard-Jonesseringused as a model approximation for van der Waals force as a function of time. Van der Waals interactions were observed on noble gas, which is very stable and tend not to interact. This explains the difficulty of the noble gases condense. However, the bigger the size of noble gas atoms (more electrons), the easier the gas turned into liquid.

2. Pull Style Dipoles

Molecules that have a permanent dipole moment said to be polar. Notice in the picture :

 

 Fig. Tri-atomic molecule polar and non polar 

Vector direction toward a more electronegative atom plus end shows to the less electronegative atom. Style attraction between two polar molecules called dipoles attraction Style. This attraction is stronger than the attraction between non-polar molecules.