Here's why:

* Central Atom: The central atom in COS is carbon (C).

* Electron Groups: Carbon forms double bonds with both oxygen (O) and sulfur (S). This means there are two electron groups around the carbon atom.

* VSEPR Theory: According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, two electron groups around a central atom will arrange themselves as far apart as possible, resulting in a linear shape.

Therefore, the COS molecule has a linear shape with the carbon atom in the middle and the oxygen and sulfur atoms on either side.