[Alcoinito]

BeF₂ and BF₃ both are stable yet each has incomplete octet. Explain. Also ascertain why BeF₂ is more stable of the two.

I am aware that these molecules are exceptions to the octet rule. But "explaining why" has particularly stumped me. I have googled my problem, and have also checked  reference book "Inorganic chem" by J.D.Lee, but to no avail.
I would be glad if someone could help me 

[gertrudetrumpet]

i think it is because the fluorine does share electrons with the boron and beryllium. it undergoes resonance. The beryllium is more stable because both fluorine share their electrons, creating a balance in charge. Also, since the molecular is linear, there is less electron repulsion between the fluorines.

[DevaDevil]

Beryllium is a metal, this makes Beryllium Fluoride a salt, aka an ionic compound. (Beryllium fluoride  has a crystal lattice in which each beryllium is surrounded by 4 fluorides)

[408]

BF3 has short B F bonds.  electrons in p orbitals on F are perpendicular to the planar BF3 molecule.  These two factors combined means the p electron density has significant overlap with the empty p orbital on B, partially filling it.