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Home » Class 11 » Chemistry » Chemical Bonding and Molecular Structure » Fajan’s Rules

Fajan’s Rules

Last Updated on February 16, 2023 By Mrs Shilpi Nagpal

When a cation approaches an anion, the electron cloud of the anion is attracted towards a cation and hence gets distorted. The effect is called polarisation of the anion.

The power of cation to polarise anion is called its polarising power and tendency of the anion to get polarised is called polarisability. The greater is the polarisation produced, more is the neutralisation of the charges and hence the ionic character decreases or the covalent character increases.

The polarising power of the cation and the polarisability of the anion and hence the formation of covalent bond depends on:

1) Small size of the cation

Smaller the cation, greater is its polarising power.

2) Large size of the anion

larger the anion, greater is its polarisability. Covalent character of lithium halides is in the order:

LiI > LiBr > LiCl> LiF

3) Large charge on the cation or anion

Larger the charge on the cation, greater is its polarising power. Hence covalent character increases .

The covalent character of the chlorides is in the order:

NaCl < MgCl2 < AlCl3 

Greater the charge on the anion, more easily it gets polarised .

4) Electronic configuration of the cations

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.

Characteristics of covalent compounds

1) Physical States: The covalent compounds exist in all the three states i.e. solid ,liquid and gases.

2) Crystal structure :The crystal structure of covalent compounds differ from that of ionic compounds. They usually consists of molecules rather than ions.

3) Melting and boiling point: Covalent compounds have low melting and boiling point because the molecules in covalent compounds are held together less rigidly.

4) Solubility: They are generally soluble in organic solvents but insoluble in water and other polar solvents.

5) Electrical conductivity :Since there are no free ions in covalent compounds to conduct electricity, they are bad conductors of electricity.

6) Non-ionic reactions :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.

7) Directional characteristics and isomerism: As the atoms in covalent compounds are held together by the shared electrons ,it is rigid and directional. Hence, atoms in a molecule can take up different directional arrangement and thus show structural and stereoisomerism.

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Filed Under: Chemical Bonding and Molecular Structure, Chemistry, Class 11 Tagged With: Characteristics of covalent compounds, polarisability, polarisation of the anion, polarising power

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Comments

  1. Ankit says

    August 31, 2018 at 2:03 pm

    It is very helpful thak u very much!!!

  2. Abhinav says

    September 11, 2018 at 7:34 am

    Nice one !!
    Appreciable !!
    Thank you

  3. Tanvi Mishra says

    July 20, 2019 at 8:49 pm

    Really, it was an informative page….
    Thanks a lot……

  4. Shubhangi mishra says

    August 28, 2019 at 7:52 pm

    Actually I wanted to know the connection between charge on an ion and It’s melting point.

  5. Javed khan says

    July 15, 2020 at 8:51 pm

    Very easy and convincing dear. Appreciated

  6. Ilaria Mishra says

    July 26, 2020 at 5:11 pm

    Thank you so much!! This was incredibly helpful! 🙂

  7. satish kumar sharma says

    October 30, 2020 at 7:07 pm

    Shilpi, it is really the noble job done by you.

  8. Vaibhav Nimkarde says

    March 19, 2021 at 10:37 pm

    Thanks mam this is really very helpful.you are doing great job.GBU

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