Vikas TU
Last Activity: 4 Years ago
Dear student
. In the case of BF3, both boron and fluorine have their valence electrons in 2p. But in BBr3, lone pair electrons are in 4p while valence electrons of Boron are in 2p. So, the size does not match. Also, electronegativity of the halogen decreases down the group. Hence, effectiveness of back bonding with Boron decreases down the halogen group.