A σ bond arises from the straight-on overlap of two atomic orbitals. The electron density lies along the axis of the two bonded nuclei. Example: Sigma Bonding in methane, CH4 What atomic or hybrid orbital on the central I atom makes up the sigma bond between this I and an outer Br atom in iodine tribromide, IBr3 ?

sp3d

Explanation:

In IBr3, iodine is the central atom surrounded by three bromine atoms. The central iodine atom uses sp3d hybrid orbitals to overlap with the three bromine atoms to form the compound.

This overlap is straight-on giving three sigma bonds when bonded to the three bromine atoms. Electron density of each bind lies along the internuclear axis of the bond.

The compound is trigonal bipyramidal with two lone pairs.