What is a molecular dipole moment?

A. The arrangement of charge around an atom in a nonpolar molecule
B. A net cancellation of charge separation due to symmetry of the molecule
C. A separation of charge characterizing a nonpolar covalent molecule
D. A separation of charge forming a positive and a negative end of a molecule

The answers are really lousy, but I suspect your teacher wants you to raise your hand and answer D.

The correct answer is D. A separation of charge forming a positive and a negative end of a molecule.

A molecular dipole moment refers to the separation of electric charge in a molecule, resulting in a positive end and a negative end. This occurs when there is a difference in electronegativity (the ability of an atom to attract electrons) between the atoms that form the molecule.

To determine whether a molecule has a dipole moment, you can follow these steps:
1. Determine the molecular geometry or shape of the molecule. This is determined by the arrangement of atoms around the central atom(s) and the number of lone pairs of electrons.
2. Determine the electronegativity of each atom in the molecule. Electronegativity values can be found on the periodic table.
3. If the molecule is symmetrical (i.e., it has the same atoms or groups of atoms on both sides), evaluate whether the electronegativities on each side cancel out. If they do, the molecule is nonpolar and does not have a dipole moment.
4. If the molecule is asymmetrical (i.e., it has different atoms or groups of atoms on each side), evaluate whether the electronegativities on each side do not cancel out. If they do not cancel out, the molecule is polar and has a dipole moment.

In this case, answer choice A is incorrect because a nonpolar molecule does not have an arrangement of charge around an atom. Answer choice B is incorrect because a net cancellation of charge separation due to symmetry results in a nonpolar molecule without a dipole moment. Answer choice C is incorrect because a nonpolar covalent molecule does not have a separation of charge. Answer choice D is correct because it accurately describes a molecular dipole moment.