Question

A nonmetallic element of group 13, used in making bullet proof vests is extremely hard solid of black colour. It can exist in many allotropic forms and has unusually high melting point. Its trifluoride acts as Lewis acid towards ammonia. The element exihibits maximum covalency of four. Identify the element and write the reaction of its trifluoride with ammonia. Explain why does the trifluoride act as a Lewis acid.

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Answer 1

Explanation:

The only non-metallic element of group 13 is boron. It is an extremely hard black subtance and is used iin making bullet proof vests. It exists in many allotropic forms and has usually high melting point. Since B has only s- and p-orbitals but no d-orbitals therefore at the maximum it can exhibit a covalency of four.

Answer 2

Answer:

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BORON

• Non-metallic element of group 13 is boron. It is grey-black and very hard in nature. It has a high melting point,2300∘C.It exists in two allotropic forms: (a) crystalline solid(b) amorphous powder.
• It forms trifluoride, BF3.BF3 acts as a Lewis acid as it is an electron deficient compound.

• $BH _{3} + NH_{3} → H _{3} N + BF_{3}$
• Here, NH3 donates an electron pair which is accepted by boron to saturate its outer shell. Maximum covalency of boron is four as its valency shell contains only four orbitals.

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