FAJAN RULE PDF

This phenomenon of distorting electron cloud of the negative ion by the positive ion is called Polarization. Now, what inference can you draw from this? The negative charge will become less negative as some of the electron cloud has migrated towards positive ion and positive ion will also become less positive as it now has more electrons then it had before. An ion of highly electropositive element will draw electron towards it with greater force and hence will create more polarization.

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Fajan rule Change of Ionic Character to Covalent Character When two oppositely charged ions of unequal size approach each other closely during formation of an electrovalent bond , the ion smaller in size attracts outermost electrons of the other ion and repel its nuclear charge. The net result is distortion or polarisation of the bigger ion. This distortion is usually done by the cation as its size is smaller than the anion.

The electron cloud of anion no longer remains symmetrical but is elongated towards the cation. The ability of a cation to polarise the nearby anion is called its Polarising power and the tendency of an anion to get distorted or deformed or polarised by the cation is called its Polarisability. Due to polarisation, sharing of electrons occur between two ions to some extent and the bond shows some covalent character. This is shown in figure. The magnitude of polarisation depends upon a number of factors or the increased covalent character is favoured by a number of factors.

This explains why LiCl is more covalent than KCl. It is due to the fact that the outer electrons of a large anion are loosely held and hence can be more easily pulled out by the cation. This explains why iodides, among halides, are most covalent in nature. C Large Charge on Either of the Two Ions: As the charge on the ion increases, the electrostatic attraction of the cation for the outer electrons of the anion also increases, with the result its ability for forming the covalent bond increases.

The percentage of ionic character in a compound having some covalent character can be calculated by the following equation. Calculate the dipole moment of KCl molecule if there were opposite charges of one fundamental unit located at each nucleus.

From the octet rule HF should have been a purely covalent compound but actually it has some amount of ionic character in it, which is due to the electronegativity difference of H and F. Thus it can be clearly seen that although we call HCl and HF as covalent compounds but it has got appreciable amount of ionic character. So from now onwards we should call a compound having more of ionic less of covalent and vice versa rather than fully ionic or covalent.

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Fajans Rule

Fajan rule Change of Ionic Character to Covalent Character When two oppositely charged ions of unequal size approach each other closely during formation of an electrovalent bond , the ion smaller in size attracts outermost electrons of the other ion and repel its nuclear charge. The net result is distortion or polarisation of the bigger ion. This distortion is usually done by the cation as its size is smaller than the anion. The electron cloud of anion no longer remains symmetrical but is elongated towards the cation.

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Fajan’s Rule – Detailed Chemistry Notes for Engineering Entrance Exams!

That positive charge then exerts an attractive force on the electron cloud of the other ion, which has accepted the electrons from the aluminium or other positive ion. Two contrasting examples can illustrate the variation in effects. In the case of aluminium iodide an ionic bond with much covalent character is present. The large charge pulls on the electron cloud of the iodines.

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