POLARISATION OF IONS: (COVALNET CHARACTER IN IONIC BONDS), POLARISING POWER OF CATION, POLARISABILITY OF ANION, BOND POLARITY & REACTIVITY, BOND ENERGY

 

POLARISATION OF IONS: (COVALNETCHARACTER IN IONIC BONDS).

             A pure ionic bond is formed when there is a complete transference of electrons takes place. The ions formed are perfect spheres.

However, positive charge on the cation has an ability to attract electrons cloud from the anion toward itself. This results in the distortions of the anion. This distortion is known as polarization. This ability of a cation to attract electron cloud and distort an anion is called its polarizing power. On the other hand the ease in which electron cloud of an anion can be distorted is called polarizability. Hence, the degree of polarization of an ionic bond refers to degree of covalency in an ionic bond.

 The distorted or polarized electron cloud of anion. Polarisation brings more electron cloud between the ionic nuclei and thus produces a significant degree of covalent bonding between the ions. When this occurs, the molecule still has separation of positive and negative charge. The molecule has an electric dipole. Hence it is called as polar molecule. Such ionic compounds are predominantly covalent.

 POLARISING POWER OF CATION:

             Cation (positive ion) smaller in radius and highly charged gives the cation a high charge density and therefore a high polarizing power. e.g; AL³⁺, B³⁺, Be²⁺, Mg²⁺, Li¹⁺ etc.

 POLARISABILITY OF ANION:

             Anion (negative ion) with greater charge and large radius are more easily polarized. Thus large anion possesses a high degree of polarisability because in larger anions electrons are situated away from the nucleus and less under the control of nucleus and less under the control of nucleus. The highly polarisable anions are I^1-, Br^1-, CL^1- and O^2- ets.     

 QUESTION:

Explain why aluminum oxide shows amphoteric properties?

SOLUTION:

 Ionic oxides are basic whereas non-metal oxides are acidic in nature. As aluminum ion, AL3+ is small and highly charged i.e; having high charge density. Hence, it can distort the electron cloud of the oxide ion causing the oxide to show both ionic and covalent characters. Due to this reason aluminum oxide have both acidic and basic properties i.e; it is amphoteric oxide. 

 QUESTION:

             Explain why aluminum chloride is soluble in benzene (organic solvent)?

 SOLUTION:

             Aluminum ion, Al³⁺ due to high charge density polarize the chloride ions. Hence it is predominantly changed into covalent compound. Due to covalent character aluminum chloride ions. Hence it is predominantly changed into covalent compound. Due to covalent character aluminum chloride is soluble in organic solvent like benzene.  Aluminum chloride is a subline salt, it also proves that it is covalent compound.

 BOND POLARITY & REACTIVITY:

             Polar molecules are more reactive than non-polar molecules. For example, both nitrogen and carbon mono oxide molecules contain triple covalent bond which require almost a similar amount of energy to break them (The co bond actually requires more energy than the N₂). However carbon mono oxide is more reactive than nitrogen molecule. Non-polar nitrogen will undergo reactions only at high temperature or in the presence of a catalyst. Carbon mono oxide which is a polar molecule burns in air to form CO₂. It also react more strongly with iron of Hemoglobin than oxygen. Some chemical reactions starts due to polar molecules. Other important polar molecules are water ammonia chlorobenzene etc.

BOND ENERGY:

             The energy required to break one mole of the bond in the gaseous molecules into gaseous atoms is called bond energy bond enthalpy. The strength of a covalent bond energy i.e; the stronger the bond, the higher the bond energy.

                         Bond               Bond Energy (K Joule^-1)

                        C – C                347

                        C = C               612

                        C C               805

             The strength of a covalent bond depends the electrostatic forces of attraction between shared pair of electrons and the nuclei. Hence, the greater the number of shared electron pairs, the stronger the covalent bond and greater is the bond energy.

                         C  C                 C   C               C    C

             The order of bond energy or bond strength is given below:

                         C – C < C = C < C  C

   

            Increasing bond energy or bond strength.