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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Hence, atoms in a molecule can take up different directional arrangement and thus show structural and stereoisomerism. Now, if we take a different example, for example AlF 3 Aluminium Fluoride.
Thus it can be seen that while HI is essentially ryles, HCl has significant ionic character.
The fluorine’s electron cloud is definitely less shielded from the nuclear charge and will thus be less polarizable. Faajns crystal structure of covalent compounds differ from that of ionic compounds. Practise s of questions mapped to your syllabus.
The ionic character arises from the polarizability and polarizing effects of H and I. 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.
Because if this electron cloud of anion is more diffused. This results in synchronised motion of the electrons and an attraction between them. Die Eigenschaften salzartiger Verbindungen und Atombau”. Electronic configuration of the cation: 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.
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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. The covalent character is found in compounds which have high polarizing cation and high polarizable anion. In inorganic chemistryFajans’ rulesformulated by Kazimierz Fajans in   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.
By Fajans’ Rules, compounds are more likely to be ionic if: 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.
Views Read Edit View history. Covalent compounds have low melting and boiling point because the molecules in covalent compounds are held together less rigidly. If the anions were different, then the answer could be affected by the variation of the anion. The users who voted to close gave this specific reason: When more molecules interact these induced dipoles lead to intermolecular attraction.
Here the significant difference between the cations is in their electronic configurations. If two cations have the same size and charge, then the one with 18 electrons in the outermost shell has greater polarising power than the other with 8 electrons in the outermost shell.
Jj Thomson Atomic Theory. The polarizing power and polarizability that enhances the formation of covalent bonds is favoured by the following factors: From Wikipedia, the free encyclopedia. The greater is the polarisation produced, more is the neutralisation of the charges and hence the ionic character decreases or the covalent character increases.
When two molecules are close together, the instantaneous dipole of one molecule can induce a dipole in the second molecule. To use Fajans’ Rules, assume your binary compound is ionic and identify the potential cation and anion. Home Questions Tags Users Unanswered.
The covalent compounds exist in all the three states i. For high fajanz, small cation will have more polarizing power. We see that a similar situation occurs, but instead of iodine we now have fluorine, a relatively small highly electronegative atom.
As the atoms in covalent compounds are held together by the shared electrons ,it is rigid and directional. They are generally soluble in organic solvents but insoluble in water and other polar solvents. Where as larger is the size of anion, more will be the polarization of anion.
Fajans Rule | Disclosing Covalent Characteristics In Ionic Bonds
Compounds are more likely to be covalent if: These compounds are molecular in nature and not ionic, their reactions are molecular and proceed at a much slower rate than those of ionic compounds. The forces involved in these cases are called London dispersion forces after Fritz Wolfgang London, To picture how 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.
Note that Fajans’ Rules have been largely displaced by Pauling’s approach using electronegtivites. Based on Fajan’s rules, it is expected that every ionic compound will have at least some amount of covalent character.
In general they increase with increasing atomic number.
Practise This Question The acid formed when sulphur trioxide reacts with water is. Login to track and save your performance. The deciding factor must be the cation. In this case, the aluminium ion’s charge will “tug” on the electron cloud of iodine, drawing it closer to itself. 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 fajasn the molecules.
Fajans’ Rule – Disclosing Covalent Characteristics in Ionic Bonds
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. How fanans I ask homework questions on Chemistry Stack Exchange? What Is Valence Bond Theory. In the case of aluminium iodide an ionic bond with much covalent character is present. Fajajs 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.