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The trend of attaining covalent character by ionic compounds as a consequence of polarisation may be generalized in terms of Fajan’s rule. According to this. Fajans’ Rule for the prediction of relative nonpolar character. Electrostatic forces in a crystal Learn Fajans’ Rule by Disclosing Covalent Characteristics in Ionic. Fajan Rule: Greater is the polarization, greater is the covalent character. | Online Chemistry tutorial IIT, CBSE Chemistry, ICSE Chemistry, engineering and.

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Home Questions Tags Users Unanswered. The various types of these interactions span large differences in energy and for the halogens and interhalogens are generally quite small.

Based on Fajan’s rules, it is expected that every ionic compound will have at least some amount of covalent character. If two cations have the same size and charge, then the one with 18 electrons in the outermost fajwns has greater polarising power than the other with 8 electrons in the outermost shell.

Let us consider AlF 3this is an ionic bond which was also formed by transfer of electron.

Fajan’s Rules | Chemical Bonding and Molecular Structure, Chemistry, Class 11

Retrieved from ” https: This explains why for the common halides, iodides, are the most covalent in nature I – pm. They can be summarized in the rles table: The fluorine’s electron cloud is definitely less shielded from the nuclear charge and will thus be less polarizable.


The changes seen in the variation of MP and BP for the dihalogens and binary interhalogens can be attributed to the increase in the London dispersion forces of attraction between the molecules. This question appears to be off-topic. In general they increase with increasing atomic number.

Fajans’ Rule – Disclosing Covalent Characteristics in Ionic Bonds

Thus covalency increases in the order: Fajans’ rule states that a compound with low positive charge, large cation and small anion has ionic bond where as a compound with high positive charge, small cation and large anion are covalently bonded.

Two contrasting examples can illustrate the variation in effects. This means a comparison needs to be made between a noble gas core and pseudo noble gas core, which as noted above holds that the pseudo noble gas would be the more polarizing. Practise This Question The acid formed when sulphur trioxide reacts with water is.

Comments It is very helpful thak u very much!!! Jj Thomson Atomic Theory. In the case of aluminium iodide an ionic bond with much covalent character is present.

The covalent compounds exist in all the three states i. Hence covalent character increases. The covalent character is found in compounds which have high polarizing cation and high polarizable anion. Because if this electron fajns of anion is more diffused.

Note that Fajans’ Rules have been largely displaced by Pauling’s approach using electronegtivites.

When more molecules interact these induced dipoles lead to intermolecular attraction. As the atoms in covalent compounds are held together by the shared electrons ,it is rigid and directional. You have selected the wrong answer!! To picture fajaans this occurs, compare the situation 1 where the electrons are evenly distributed and then consider 2 an instantaneous dipole that would arise from an uneven distribution of electrons on one side of the nucleus.


The effect is called fajanw of the anion. Covalent compounds have low melting and boiling point because the molecules in covalent compounds are held together less rigidly.

Fajans’ rules

Intermolecular forces are the attractive forces between molecules without which all substances would be gases. In reality, every bond has some covalent as well as ionic characteristics. Fajans’ rules note the difference were formulated in by Kazimierz Fajans. Now, if we consider the iodine atom, we see that it is relatively large and thus the outer shell electrons are relatively well shielded from the nuclear charge.

From fajanns it is possible to calculate a theoretical dipole fakans for the KBr molecule, assuming opposite charges of one fundamental unit located at each nucleus, and hence the percentage ionic character of KBr.

The ability of a cation to distort an anion is known as its polarization power and the tendency of the anion to become polarized by the cation is known as its polarizability. Larger the charge on the cation, greater is its polarising power.