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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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. When more molecules interact these induced dipoles lead to intermolecular attraction. This produces an ionic bond with covalent character. The forces involved in these cases are called London dispersion forces after Fritz Wolfgang London, Now, if we take a different example, for example AlF 3 Aluminium Fluoride.
Leave a Reply Cancel reply Your email address will not be published. If the anions were different, then the answer could be affected by the variation of the anion.
For high charge, small fzjans will have more polarizing power.
They can be summarized in the following table:. We see that a similar situation occurs, but instead of iodine we now have fluorine, a relatively small rule electronegative atom. 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.
Fajans’ rules note the difference were formulated in by Kazimierz Fajans.
Fajans’ rules – Oxford Reference
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. The changes seen in the variation of Famans and BP for the dihalogens and binary interhalogens can be attributed to the increase in the London dispersion forces of attraction between the molecules. They are generally soluble in organic solvents but insoluble in water and other polar solvents.
In this article, we are going to discuss covalent characteristics in ionic bonds. The greater is the polarisation produced, more is the neutralisation of the charges and hence the ionic character decreases or the covalent character increases.
In general they increase with increasing fakans number.
This page was last edited on 18 Novemberat To picture how this occurs, compare the situation 1 where the electrons fajasn evenly distributed and then consider 2 an instantaneous dipole that would arise from an uneven distribution of electrons on one side of the nucleus.
In the case of aluminium iodide an ionic bond with much covalent character is present.
When a cation approaches an anion, the electron cloud of the anion is attracted towards a cation and hence gets distorted. Hence covalent character increases.
Let rulex consider AlI 3 ; this is an ionic bond which was formed by transfer of electrons. Electronic configuration of the cation: The crystal structure of covalent compounds differ from that of ionic compounds.
It is found that the greater the possibility of polarization, the lower is the melting point and heat of rhles and the greater is the solubility in non-polar solvents.
The various types of these interactions span large differences in energy and for the halogens and rulws are generally quite small. The users who voted to close gave this specific reason: This makes the anion easily polarizable. 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. Here the significant difference between the cations is in their electronic rulss.
The covalent compounds exist in all the three states i. Larger the charge on the cation, greater is its polarising power. In reality, every bond has rupes covalent as well as ionic characteristics. Thus covalency increases in the order: Gas To Solid Is Called. Two contrasting examples can illustrate the variation in effects. The covalent character is found in compounds which have high polarizing cation and high polarizable anion.
The effect is called polarisation of the anion. Intermolecular forces are the attractive forces between molecules without which all substances would be gases. As the atoms in covalent compounds are held together by the shared electrons ,it is rigid and directional.
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