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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They are derived from momentary oscillations of electron charge in atoms and hence are present between all particles atoms, ions and molecules.

The crystal structure of rlues compounds differ from that of ionic compounds. The forces involved in these cases are called London dispersion forces after Fritz Wolfgang London, Practise s of questions mapped to your syllabus. This question appears to be off-topic. For help asking a good homework question, see: They can be summarized in the following table: The various types of these interactions span large differences in energy and for the halogens and interhalogens are generally quite small.

In reality, every bond has some covalent as well as ionic characteristics.

To use Fajans’ Rules, assume your binary compound is ionic and identify the potential cation and anion. 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.

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. On the left, the cation charge increases size decreases and on the right, the anion size increases, both variations leading to an increase in the covalency. From the Table below the observed dipole moment of KBr is given as In this case, the aluminium ion’s charge will “tug” on the electron cloud of iodine, drawing it closer to itself.


The fluorine’s electron cloud is definitely less shielded from the nuclear charge and will thus be less polarizable. Congratulations You have selected the correct answer!! However, the remnants of Fajans’ Rules are found in Hard-Soft Acid-Base Theorywhich predicts bonding properties based on polarizability which is based on size and charge. Because if this electron cloud of anion is more diffused.

As the atoms in covalent compounds are held together by the shared electrons ,it is rigid and directional. 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. When more molecules interact these induced dipoles lead to intermolecular attraction. Now, if we take a different example, for example AlF 3 Aluminium Fluoride.

By Fajans’ Rules, compounds are more likely to be ionic if: Home Questions Tags Users Unanswered.

Fajans’ rules

Take learning on the go with our mobile app. Gas To Solid Is Called. As the electron cloud of the iodine nears the aluminium atom, the negative charge of the electron cloud “cancels” out the positive charge of the aluminium cation. In inorganic chemistryFajans’ rulesformulated by Kazimierz Fajans in[1] [2] [3] are used to predict whether a chemical bond will be covalent or ionicand depend on the charge on the cation and the relative sizes of the cation and anion.

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

Jj Thomson Atomic Theory. The covalent compounds exist in all the three states i. Thus it can be seen that while HI is essentially covalent, HCl has significant ionic character. The greater is the polarisation produced, more is the neutralisation of the charges and hence the ionic character decreases or the covalent character increases.

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 fajjans ion. Hence covalent character increases.


For high charge, small cation will have more polarizing power. What is Fajans rule?

Fajans’ Rule – Disclosing Covalent Characteristics in Ionic Bonds

It is found that the greater the possibility of polarization, the lower is the melting point and heat of sublimation and the greater is the solubility in non-polar solvents. The changes seen in the variation of MP and BP for the dihalogens and binary interhalogens can fajsns attributed to the increase in the London dispersion forces of attraction between the molecules.

We see that a similar situation occurs, but instead of iodine we now have fluorine, a relatively small highly electronegative atom. The “size” of the charge in an ionic bond depends on the number of electrons transferred.

Chemistry Stack Exchange works best with JavaScript enabled. This fajabs the anion easily polarizable. Based on Fajan’s rules, it is expected that every ionic compound will have at least some amount of covalent character. From Wikipedia, the free encyclopedia. This produces an ionic bond with covalent character. Leave a Reply Cancel reply Your email address will not be published. The percentage of ionic character in a compound can be estimated from dipole moments.

If the anions famans different, then the answer could be affected by the variation of the anion.

Fajans Rule | Disclosing Covalent Characteristics In Ionic Bonds

Login to track and save your performance. Let us consider AlF 3this is an ionic bond which was also formed by transfer of electron. They usually consists of molecules rather than ions. Since there are no eules ions in covalent fajan to conduct electricity, they are bad conductors of electricity.

The covalent character is found in compounds which have high polarizing cation and high polarizable anion. Boiling Point Of Oxygen. On average the electron cloud for molecules can be considered to be spherical in shape.