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Suggest reasons why the B-F bonds lengt...

Suggest reasons why the B-F bonds lengths in `BF_3` (130 pm) and `BF_4^-` (143 pm ) differ.

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In `BF_3` there is back bonding. Boron accepts a pair of electrons from fluorine to complete octet. `BF_3` exists in the following resonance structures due to back bonding . Due to the resonance hybridisation each B-F bond gets some double bond character. So the B-F length will be less than the sum of the covalent radii of boron and fluorine.

In `BF_4^-` there is no back bonding. So there is no double bond character . This is because in `BF_4^-` boron already had octet. Hence the B-F bond length in `BF_4^-` is greater than in `BF_3`.
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VGS PUBLICATION-BRILLIANT-THE P-BLOCK ELEMENTS - GROUP 13 -SHORT ANSWER QUESTIONS
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  7. What happens when Boric acid is added to water ?

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  8. What happens when Aluminium is heated with dilute NaOH ?

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  14. Give reasons Aluminium utensils should not be kept in water overnigh...

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  17. Explain borax bead test with a suitable example

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  18. Explain the structure of diborane.

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