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A non-metallic element of group 13, used...

A non-metallic element of group 13, used in making bullet prrof vests is extremely hard solid of black colour. It can exist in many allotroic forms and has unusally high melting point. Its trifluoride acts as Lewis acid towards ammonia. The element exhibits maximum covalency of four. Identify the element and write the reaction of tits triffuoride with ammonia. Explain why does the trifuoride act as Lewis acid.

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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.

Since B in `BF_(3)` has only six electrons in its valence shell, therefore, it needs two more electrons to complete its octet. Thus, `BF_(3)` acts as a Lewis acid.
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