Here's why:

* Electronegativity: Fluorine is the most electronegative element, while beryllium has a relatively low electronegativity. This large difference in electronegativity means that fluorine attracts the shared electrons in the bond much more strongly than beryllium.

* Ionic vs. Covalent: While the electronegativity difference is significant, it's not large enough to form a purely ionic bond. The shared electrons are more closely associated with fluorine, but they are still shared, resulting in a polar covalent bond.

Polar Covalent Bond:

This means the bond has a partial positive charge (δ+) on the beryllium atom and a partial negative charge (δ-) on the fluorine atom. This creates a dipole moment within the BeF₂ molecule.