The dipole moments of CCl4, CHCl3 and CH4 are in the order :
The dipole moment is a measure of the polarity of a molecule, determined by the magnitude of the charge separation and the distance between the charges. It is a vector quantity, so the overall dipole moment of a molecule depends on both the individual bond dipoles and the molecular geometry.
Let's analyze each molecule:
CH4 (Methane): It has a tetrahedral geometry. The C-H bonds are polar, but because the molecule is perfectly symmetric, the individual bond dipoles cancel each other out. Therefore, the net dipole moment is zero.
CCl4 (Carbon tetrachloride): It also has a tetrahedral geometry. The C-Cl bonds are polar (chlorine is more electronegative than carbon), but again, due to the symmetric arrangement, the vector sum of all bond dipoles is zero. Its net dipole moment is also zero.
CHCl3 (Chloroform): It has a tetrahedral geometry, but it is not symmetric. Three chlorine atoms and one hydrogen atom are attached to the central carbon. The C-Cl bonds have a significant dipole moment, and the C-H bond has a smaller one in the opposite direction. The three C-Cl bond dipoles do not cancel each other out, and their resultant has a specific direction. The C-H dipole is too small to cancel this large resultant. Therefore, CHCl3 has a substantial net dipole moment.
Conclusion: Both CH4 and CCl4 have a net dipole moment of zero due to their symmetric structures. CHCl3 is asymmetric and has a significant dipole moment. Thus, the correct order is CH4 = CCl4 < CHCl3.
Dipole Moment (μ): The dipole moment is calculated using the formula: , where Q is the magnitude of the charge separated and d is the distance between them. Its SI unit is the Debye (D).
Molecular Polarity: A molecule's overall polarity depends on two factors: the polarity of its individual bonds (determined by the difference in electronegativity between the bonded atoms) and the shape of the molecule (its symmetry). A molecule can have polar bonds but be non-polar overall if its geometry allows the bond dipoles to cancel out.
VSEPR Theory: Valence Shell Electron Pair Repulsion theory is used to predict the geometry of molecules, which is crucial for determining the vector sum of bond dipoles.
