Question

How you can explain that `C Cl_4` has no dipole moment?

Answer 1

Well, the molecular dipole moment....

Explanation:

....is the vector sum of the individual bond dipoles. There is some difference in negativity between carbon and chlorine, enuff to give a `""^(+delta)C-Cl^(delta-)` dipole, but when these dipoles are summed together in a vector fashion, the resultant is ZERO......

On the other hand, chloroform, `"HCCl"_3`, which is more of less identical to carbon tet. geometrically, is a polar molecule, because the vector sum of the individual bond dipoles DOES NOT sum to ZERO.

Answer 2

See below...

Explanation:

Let's have a vector approach.

• The angle between two `"Cl"` atom is always `color(red)(109^@28'`.
• So, we have to take the cos component of the three `"Cl"` atoms showing in the pic downside.
• I mark the upper one as `(1)`, left one as `(2)`, bottom one is `(3)` and the right one is `(4)`.

For `(2),(3),(4)` no. chlorine,the resultant dipole moment is

#mu_((2-3-4))=3xxmu_1 cdot cos(180^@-109^@28')=3xxmu_1xx0.333=3xxmu_1xx1/3=mu_1" "#[`mu_1` is generated dipole moment for each `"Cl"` atom.]

Now, the upper `"Cl"` atom's dipole moment and the resultant dipole moment cancel out each other.

Hence,`color(red)(mu_("CCl"_4))=mu_1-mu_1=0`

This is the answer proved by vector.