Boron fluoride exists as BF3 but boron hydride doesn't exist as BH3. Give reason. In which form does it exist? Explain its structure.

This is a Long Answers Type Questions as classified in NCERT Exemplar 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 -centered- 2 -electron bond.

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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Alok Kumar Singh | Contributor-Level 10

8 months ago

This is a Long Answers Type Questions as classified in NCERT Exemplar

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 di

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(i)→ (b), (ii) → (c), (iii) → (b), (iv) → (a) (v)→ (b) (vi)→ (c)

Match the species given in Column I with properties given in Column II.

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(a) Used as a flux for soldering metals

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(i)→ (c) (ii)→ (d) (iii)→ (a) (iv)→ (e) (v)→ (b)

Match the species given in Column I with the properties mentioned in Column II.

Column I

Column II

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(a) Oxidation state of central atom is +4

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(i)- (e), (ii)- (c), (iii)- (d), (iv)- (a) & (b)

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Chemistry NCERT Exemplar Solutions Class 11th Chapter Eleven 2025

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(i) Boron in [B(OH)₄]⁻	(a) sp²
(ii) Aluminium in [Al(H₂O)₆]³⁺	(b) sp³
(iii) Boron in B₂H₆	(c) sp³d²
(iv) Carbon in Buckminsterfullerene
(v) Silicon in SiO₄⁴⁻
(vi) Germanium in [GeCl₆]²⁻

Column I	Column II
(i) Diborane	(a) Used as a flux for soldering metals
(ii) Gallium	(b) Crystalline form of silica
(iii) Borax	(c) Banana bonds
(iv) Aluminosilicate	(d) Low melting, high boiling, useful for measuring high temperatures
(v) Quartz	(e) Used as catalyst in petrochemical industries.

Column I	Column II
(i) BF₄⁻	(a) Oxidation state of central atom is +4
(ii) AlCl₃	(b) Strong oxidising agent
(iii) SnO	(c) Lewis acid
(iv) PbO₂	(d) Can be further oxidised
	(e) Tetrahedral shape