# Why does boron trifluoride behave as a Lewis acid?

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Why does boron trifluoride behave as a Lewis acid?

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The B atom in BF3 has only 6 electrons in the valence shell and thus needs two more electrons to complete its octet. Therefore, it easily accepts a pair of electrons from nucleophiles such as F- , NH3 , (C2H5)2O, RCH2OH etc. and thus behaves as a Lewis acid.