Power point Presentation On intermolecular forces

Power point Presentation On : 

Power point Presentation On INTERMOLECULAR FORCES

INTERMOLECULAR FORCESDefinition : 

INTERMOLECULAR FORCESDefinition Intermolecular Forces of attraction and repulsion occur between interacting particles (atoms or molecules). These exist in all states of matter and are responsible for many structural features and physical properties of matter. These forces does not include in them the electrostatic forces that exist between oppositely charged ions and the forces that hold atoms of a molecule together i.e., covalent bonds.

INTERMOLECULAR FORCESCharacteristics : 

INTERMOLECULAR FORCESCharacteristics The intermolecular forces are weak forces. These are present even in case of non-polar molecules such as SO2,CO2,Cl2,CH4 etc. , in the solid and liquid states. These forces also operate in the liquid state of noble gases which are mono atomic and stable. Such forces come into existence due to the interplay of the positive and negative charges between the neighboring atoms of non-polar molecules when they are very close to each other.

INTERMOLECULAR FORCESTypes of Interactions : 

INTERMOLECULAR FORCESTypes of Interactions The existence of these weak intermolecular forces was first proposed by the Dutch scientist Johannes van der Waals. Intermolecular forces arise due to the following types of interactions : London Forces or dispersion forces Dipole Dipole Forces Dipole- Induced Dipole Forces Hydrogen Bonding

LONDON FORCESDefinition : 

LONDON FORCESDefinition The force of attraction between an instantaneous dipole and an instantaneous induced dipole is called London Forces or dispersion forces. These forces occur in non-polar molecules and even in noble gases. These forces of attraction were first studied and proposed by the German physicist Fritz London and therefore these are known as London Forces.

LONDON FORCESHow These Occur : 

LONDON FORCESHow These Occur The electron cloud in atoms and non-polar molecules is symmetrically distributed and thus have no dipole moment. If due to the motion of the electrons the electronic charge becomes unsymmetrical, as a result of this an instantaneous dipole is created. This instantaneous dipole distorts the electron distribution in the neighboring atom and induces a dipole called instantaneous induced dipole.

LONDON FORCESAffecting Factors : 

LONDON FORCESAffecting Factors The interaction energy due to these forces is proportional to the sixth power of the distance between two interacting particles . These forces are significant only at short distances of about 500 pm. These also depend upon the polarisability of the atom or a molecule. Polarisability is the measure of the ease with which the electrons and nuclei can be displaced from their average positions.

LONDON FORCES (Continued) : 

LONDON FORCES (Continued) The strength of the London forces depends upon the following :- Size of the molecule- large molecules have much diffused charged clouds so there are great chances of its distortion and producing instant dipoles. Number of electrons in the molecule- larger the number of electrons in the atom or molecule , the larger is the charge on one side and the larger is the chance of formation of instantaneous dipoles. Molecular structure- the strength increases with the molecular size. This is evident from the boiling points of Methane (CH4), Silane (SiH4) and Germane (GeH4) which increase from 112K to 161K to 183K respectively due to increase in molecular size. Polarisability- more the polarisibility of the atom or molecule greater is the magnitude of instantaneous dipole and hence stronger are the London forces.

DIPOLE DIPOLE FORCESDefinition : 

DIPOLE DIPOLE FORCESDefinition The force of attraction between the molecules having permanent electric dipoles is called dipole dipole forces. These forces occur between polar molecules having separate centres of positive and negative charges and the dipoles posses “partial charges”. These partial charges are always less than the unit electronic charge (1.6 * 10^-19 C). These forces are stronger than the London forces.

DIPOLE DIPOLE FORCESHow They Occur : 

DIPOLE DIPOLE FORCESHow They Occur Suppose there are two HCl molecules having permanent dipole with partial negative and positive charges. The positive end of one molecule attracts the negative end of the other molecule and vice-versa. Greater the dipole moment of the molecules greater is the forces of attraction . This effect is called Orientation Effect. This effect was first studied by Willem Hendrick Keesom and the dipole dipole forces are called Keesom Forces.

DIPOLE DIPOLE ForcesAffecting Factors : 

DIPOLE DIPOLE ForcesAffecting Factors Dipole Dipole interaction energy between stationary polar molecules (as in solids in the figure below) is proportional to the third power of the distance between two interacting particles and that between rotating polar molecules is proportional to the sixth power of the distance between two particles. Due to the involvement of only partial charges the interaction decrease with the increase of the distance between dipoles. Besides dipole dipole forces the polar molecules can interact by London forces also hence resulting in the cumulative effect of increase in the total intermolecular forces.

DIPOLE – INDUCED DIPOLE FORCESDefinition : 

DIPOLE – INDUCED DIPOLE FORCESDefinition The force of attraction operating between the polar molecule having permanent dipole and the non-polar molecules having no permanent dipole like BF3, SO3 etc. The polar molecule induces an electric dipole in the non-polar molecule resulting in attraction of the two molecules. These forces were studied by Debye in 1920.

DIPOLE – INDUCED DIPOLE FORCESHow They Occur : 

DIPOLE – INDUCED DIPOLE FORCESHow They Occur When a polar molecule interacts with a non –polar molecule, the permanent dipole of the polar molecule distorts the electron distribution of the non-polar molecule. This causes a shift in the negative charge relative to the nuclear charge and results in the formation of induced dipole moment. Thus, these both i.e. , permanent dipole and induced dipole get attracted to form bond and this effect is called Induction Effect.

DIPOLE – INDUCED DIPOLE FORCESAffecting Factors : 

DIPOLE – INDUCED DIPOLE FORCESAffecting Factors The interaction energy is proportional to the sixth power of the distance between two interacting molecules. The strength of the force depend upon the following:- The Dipole Moment of the polar molecule – as the increase in the dipole moment will increase the dipole moment in the non-polar molecule. Polarisability – more the polarisability of the non-polar atom of molecule , more is the tendency to get induced.

HYDROGEN BONDINGDefinition : 

HYDROGEN BONDINGDefinition The force of attraction between hydrogen attached to electronegative atom of other polar molecules like H2O, HF, NH3 etc. The Hydrogen Bonding is a special case of dipole dipole interactions. This bond is weaker than the Covalent Bond.

HYDROGEN BONDINGTypes of Hydrogen Bonding : 

HYDROGEN BONDINGTypes of Hydrogen Bonding There are two types of Hydrogen Bond , namely – (1) Intermolecular Hydrogen Bond- It is formed between two different molecules of the same or different compounds. For example in case of HF, H2O etc. (2) Intramolecular Hydrogen Bond- It is formed when hydrogen atom is in between the two highly electronegative (F,O,N) atoms present within the same molecule. For example in o-nitrophenal, the hydrogen atom is in between two oxygen atoms.

HYDROGEN BONDINGHow It Occurs : 

HYDROGEN BONDINGHow It Occurs Suppose in HF molecule, hydrogen atom forms a weak bond with F atom of the neighboring molecule while remaining bonded to its F atom. In other words, hydrogen atom acts as a bridge between two atoms, holding one atom by a covalent bond (- - -) and other atom by a hydrogen bond (…..). As a result, HF exists as a cluster of hydrogen fluoride molecules.

HYDROGEN BONDINGOther Features : 

HYDROGEN BONDINGOther Features Although hydrogen bonding is regarded as being limited to N,O and F but some molecules containing Cl may also participate in hydrogen bonding. The energy of hydrogen bond varies from 10-100 KJ/mol. Therefore, hydrogen bonds are powerful force in determining the properties of many compounds like proteins and nucleic acids. The strength of hydrogen bond is determined by the coulombic interactions between the lone pair electrons of the electronegative atom of one molecule and hydrogen bond of other molecule.