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प्रश्न
Boron fluoride exists as BF3 but boron hydride doesn’t exist as BH3. Give reason. In which form does it exist? Explain its structure.
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उत्तर
In BF3, due to n – pπ back bonding between the vacant p-orbital of boron and filled p-orbital of fluorine. This π – pπ back bonding is absent in case of hydrogen as it is a single electron element.
Two BH3 molecules dimerise to form diborane.
In B2H6 There are two types of hydrogens present.
(i) Four hydrogens that are terminally bonded to each of two boron atoms.
(ii) Two hydrogens that are bonded to both boron atoms forming a bridge in between.
The four-terminal hydrogen atoms and two boron atoms lie in the same plane while bridging hydrogen lies in a plane perpendicular to them.
Two hydrogens forming a bridge in B2H6 are peculiar in bonding and can be termed as 3 -centered-2-electron bond or banana bond. 1sorbital of each hydrogen overlaps with the hybrid orbital of one of the boron then delocalising the 2e– over three atoms making 3-centred- 2 -electron bond.
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संबंधित प्रश्न
How can you explain higher stability of BCl3 as compared to TlCl3?
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Explain the following:
Boron does not exist as B3+ ion.
Explain the following:
PbX2 is more stable than PbX4.
Explain the following:
Electron gain enthalpy of chlorine is more negative as compared to fluorine.
Explain the following:
Tl (NO3)3 acts as an oxidising agent.
Match the species given in Column I with the properties mentioned in Column II.
| Column I | Column II |
| (i) \[\ce{BF^{-}4}\] | (a) Oxidation state of central atom is +4 |
| (ii) AICI3 | (b) Strong oxidising agent |
| (iii) SnO | (c) Lewis acid |
| (iv) PbO2 | (d) Can be further oxidised |
| (e) Tetrahedral shape |
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Atomic size
Describe the general trends in the following properties of the elements in Groups 13 and 14.
Metallic character
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Nature of halides
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Though fluorine is more electronegative than chlorine yet BF3 is a weaker Lewis acid than BCl3
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