Boron triiodide (BI3) is a covalent compound. It serves as a specialized reagent for cleaving C-O bonds in ethers, esters, and alcohols, and is also used to cleave silanes and halides. The Lewis structure of BI3 is similar to that of indium chloride (InCl3), consisting of a central boron atom (B) and three iodine atoms (I) symmetrically distributed around it. The boron atom is bonded to the three iodine atoms, and each iodine atom possesses three lone pairs of electrons. The specific structural formula is shown in the figure below:

How to Draw the Lewis Structure of BI3

According to the periodic table, the total number of valence electrons in the BI3 molecule is 1(3) + 3(7) = 24.

Since the electronegativity of the boron atom (B) is lower than that of the iodine atoms (I), the boron atom serves as the central atom. The total number of electron pairs is 24 / 2 = 12. Bonding the boron atom to each of the three iodine atoms requires three electron pairs. The remaining nine electron pairs are distributed equally among the three iodine atoms. In this configuration, the formal charges on both the boron atom and the iodine atoms are zero.

It is important to note that boron is an exception to the octet rule, as it can achieve stability with either eight or fewer than eight electrons in its outermost shell. Conversely, iodine atoms (I) can accommodate more than eight electrons in their outermost shell. Therefore, although the boron atom in the BI3 molecule does not satisfy the octet rule, the molecule still achieves a stable Lewis structure.