The \(\mathrm{CO}_{2}(\mathrm{OCO})\) and \(\mathrm{OCS}\) molecules are both linear. Both have polar bonds. \(\mathrm{CO}_{2}\) does not have a dipole moment (that is, the dipole moment is zero). Why does OCS have a dipole moment?

Electronegativity is a fundamental concept in chemistry, describing how strongly an atom can attract and hold onto electrons when it forms a chemical bond. On the periodic table, electronegativity values increase from left to right and bottom to top. Elements like fluorine have the highest electronegativity, while those like cesium have much lower values.

Imagine the tug-of-war over electrons during the formation of a chemical bond: the atom with higher electronegativity will win, pulling the shared electrons closer to itself. This results in the creation of polar bonds if the connected atoms have significantly different electronegativities. Understanding this concept helps explain why certain molecules possess polar characteristics while others do not.

Dipole moment is a measure of the separation of positive and negative charges in a molecule. A higher dipole moment means there is a stronger disparity in charge distribution within the molecule. It is represented both in direction and magnitude: the arrow of the dipole moment points from the positive to the negative end, highlighting the flow of electronic charge.

In the cases where molecules have symmetrical shapes, such as the linear shape of CO2, any dipole moments present due to polar bonds may cancel out, as the opposite dipoles are of equal magnitude and in opposite directions, leading to a net dipole moment of zero. This is precisely why CO2, despite having polar bonds, ends up being a non-polar molecule overall.

The linear molecular shape plays a crucial role in determining a molecule's overall polarity. When a molecule has a linear geometry, like CO2 and OCS, the angle between the bonds is 180 degrees. This arrangement means that any dipoles within the molecule could potentially cancel each other out if they are of equal magnitude and directly opposite.

However, the presence of a different atom or unequal bond strengths can disrupt this balance, resulting in a molecule with a net dipole moment, such as OCS. The key to understanding why certain linear molecules have dipole moments while others don't is to look at the electronegativity of the atoms and the symmetry of the molecule's shape.