BF3 is a molecule consisting of an sp2 hybrid of Boron covalently bonded with 3 atoms of fluorine. The covalent bond tells us that electrons are shared, rather than lost by boron and gained by fluorine.

What kind of bond is BF3?

It follows, therefore, that an atom will tend to make as many covalent bonds as possible. In the case of boron in BF3, three bonds is the maximum possible because boron only has 3 electrons to share. You might perhaps wonder why boron doesn’t form ionic bonds with fluorine instead.

BF3 is an electron-deficient compound. Boron(B) atom has 3 electrons in its outermost shell and forms 3 single covalent bonds with fluorine and attains 6 electrons.

Why is BF3 more covalent?

As the atomic size decreases, the ability or tendency to form covalent bond increases. There is a large degree of π-bonding when the halogen is Fluorine as compared to when it is Cl, Br or I. The bonding goes on decreasing subsequently. Therefore, BF₃ is more covalent in nature than others.

The central atom bromine uses the d-orbitals for hybridization. In BrF3, it will have 2 lone pairs and 3 Br—F covalent bonds.