Polar covalent molecules exhibit dipole moment. Dipole moment is equal to the product of charge separation , q and the bond length d for the bond. Unit of dipole moment is debye. One debye is equal to `10^(-18)` esu cm.
Dipole moments is a vector quantity. It has both magnitude and direction. Hence, dipole moment of a molecule depends upon the relative orientation of the bond dipoles, but not on the polarity of bonds alone. A symmetrical structure shows zero dipole moment. Thus, dipole moment helps to predict the geometry of a molecules. Dipole moment values can be distinguish between cis- and trans- isomers, ortho, meta and pare-forms of a substance, etc.
Q. `mu` of the `AX_(4)` type of molecule is zero. The geometry of it can be :

Options

A. tetrahedral
B. square planar
C. A or B
D. None of these

Answer

To determine the geometry of an `AX4` type molecule with a dipole moment (μ) of zero, we need to analyze the characteristics of such a molecule step by step.

### Step 1: Understand the `AX4` Notation
- In the `AX4` notation, 'A' represents the central atom, and 'X' represents the surrounding atoms. The subscript '4' indicates that there are four atoms bonded to the central atom.

### Step 2: Identify the Possible Geometries
- For an `AX4` type molecule, the common geometries are:
- Tetrahedral
- Square planar (for certain cases, such as when there are lone pairs)

### Step 3: Analyze the Tetrahedral Geometry
- In a tetrahedral geometry, the bond angles are approximately 109.5 degrees, and the four bonds are symmetrically arranged around the central atom.
- An example of a tetrahedral molecule is methane (CH4), where the four hydrogen atoms are symmetrically distributed around the carbon atom.

### Step 4: Determine the Dipole Moment
- The dipole moment is a vector quantity that depends on both the magnitude of the bond dipoles and their orientation.
- In a symmetrical tetrahedral molecule like CH4, the individual bond dipoles cancel each other out due to symmetry, resulting in a net dipole moment of zero.

### Step 5: Consider Other Geometries
- Another possible geometry for an `AX4` type molecule is square planar, which occurs in cases where there are lone pairs on the central atom (e.g., XeF4).
- In a square planar geometry, the four surrounding atoms are arranged in a plane, and the lone pairs are positioned above and below this plane. This arrangement can also lead to a cancellation of dipole moments, resulting in a net dipole moment of zero.

### Conclusion
- The geometry of an `AX4` type molecule with a dipole moment of zero can be either tetrahedral or square planar, depending on the presence of lone pairs on the central atom.

### Final Answer
The geometry of an `AX4` type molecule with a dipole moment of zero can be:
1. Tetrahedral
2. Square Planar

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