States of matter intermolecular forces Part -1

 

States of matter

There are two types of properties shown by individual or the collection of a large number of particles

A)        1)   Individual/atomic properties- are shown by single particle or atom of a matter

Examples- atomic size, atomic/ionic radii, ionisation enthalpy, electron gain enthalpy, electronegativity, electro positivity

B)      2). Bulk properties-

                           those properties which are associated with the collection of a large number of individual particles are called bulk properties.

Example - Melting, boiling, solubility, water having wetting properties

Water exist in three states of matter as

                                                                   Solid -     Ice

                                                                  liquid – water

                                                                  Gas - water vapour

Triple point- the state at which all three phases exists simultaneously is called triple point

i.e. there are three states of matter as         a) solid   b) liquid     c) gas

on the basis of shape, volume, rigidity, fluidity, interparticle spaces, interparticle force, K.E. and Diffusion  

Mainly, the states of matter depend upon –

                                                       1). Energies of molecules

                                                       2). On the manner in which the individual molecules bind/aggregate

Note -Chemical properties of a substance do not change with the change of its physical state but the rate of chemical reaction do depend upon the physical state.

          Therefore  ,it become necessary for a chemist to know the knowledge of state of matter and the physical laws which govern the behaviour of matter in different states

Intermolecular forces-

·       The forces of attraction and repulsion between interacting particles (atoms or molecules) are called intermolecular forces.

·       These exist all matters ( solid liquid gas)  and responsible for many structural feature and physical properties of matter.

·       this term does not involved the electrostatic/ionic force and covalent bonds

·       intermolecular forces are weaker forces.

·       The attrative intermolecular forces are known as Vander Waals forces, in honour of Dutch scientists Johannes who studied the effect of these molecular forces on the real gases

Intermolecular forces  arise due to the following type of interactions:-

1). Dispersion forces or London force or instantaneous dipole – induced dipole forces

      ·            This force of attraction was firstly proposed by the German physicist Fritz London.

      ·           Dispersion forces are weaker intermolecular forces

      ·          These forces exert among the atoms(noble gases) or molecules(H₂ O₂ N₂ CO2  which are electrically symmetrical and have no dipole moment because their electronic charge cloud is symmetrically distributed.

       ·         Temporary dipoles can occur in non- polar molecules when the electrons that constantly orbit the nucleus occupy a similar location or unsymmetrical that means the charge cloud become more on one side than the other  by chance(momentarily).it is also called instantaneous dipole.

                     This instantaneous or transient dipole distorts the electron density of the other atom or molecule.

    i.e. Temporary dipoles can induce a dipole in neighbouring molecules, initiating an attraction called London force.

·       These forces are always attractive and interaction energy is proportional to 1

2. Dipole- induced dipole interaction·       This force of attraction was firstly proposed by the German physicist Fritz London.

·       Dispersion forces are weaker intermolecular forces

·       These forces exert among the atoms(noble gases) or molecules(H₂ O₂ N₂ CO2  which are electrically symmetrical and have no dipole moment because their electronic charge cloud is symmetrically distributed.

·       Temporary dipoles can occur in non- polar molecules when the electrons that constantly orbit the nucleus occupy a similar location or unsymmetrical that means the charge cloud become more on one side than the other  by chance(momentarily).it is also called instantaneous dipole.

·       This instantaneous or transient dipole distorts the electron density of the other atom or molecule.

i.e. Temporary dipoles can induce a dipole in neighbouring molecules, initiating an attraction called London force.

·       These forces are always attractive and interaction energy is proportional to 1/r⁶

2. Dipole- diploe (Keesom) force-

     ·       This interaction was first studied by Kessom in 1912.

     ·       These forces occur in molecules which have permanent electric dipole such as HCl, NH3, H2O etc.

     ·       A polar molecule has separate centre of positive and negative charges and the ends of dipoles possess “partial charge” (δ=delta=partial)

    ·       The partial charges are always less than the unit electronics charge (1.6 X 10^-19C).

    ·       These forces arise due to interaction between oppositely charged ends of the polar molecules.

    ·       The positive end of one molecule attract the negative end of the other molecule and vice versa

     ·       Greater the dipole moment of the molecules, greater is the forces of attraction.

     ·       It is stronger than London force

      ·       Interaction energy is proportional to 1/r³ (between stationary polar molecules and is proportional to 1/r⁶

   Besides dipole-dipole interaction, polar molecule can interact by London forces also.as a result the net intermolecular forces in polar molecules increase.

4. Hydrogen Bond