Question

how does the tetrahedral shape of CHCl3 have less dipole moment than CH2Cl2

Answer 1

CH2Cl2 has the greatest dipole moment. CCl4 is the only one without a dipole. The electronegativity difference in the two atoms causes a polar bond which results in a partial charge on each atom. These molecules are in a tetrahedral configuration, so the two Cl atoms in CH2CL2 do not cancel out, they are additive. These charges act like vectors when in a magnetic field. Think of the geometry or build a model of the molecule and you will see why CHCl3 results in a lower net dipole than CHCl2