Question

Account for the fact that among the chlorinated derivatives of methane, chloromethane has the largest dipole moment and tetrachloromethane has the smallest dipole moment:

Short answer

Question: Explain why chloromethane has the largest dipole moment among the chlorinated derivatives of methane, and why tetrachloromethane has the smallest dipole moment. Answer: Chloromethane has the largest dipole moment because it has a highly polar C-Cl bond, while the dipole moment decreases in other chlorinated derivatives due to the increasing symmetry of the molecules. Tetrachloromethane has the smallest dipole moment because its completely symmetric structure results in a net dipole moment of zero.

Step-by-step solution

Define dipole moment

Dipole moment is a measure of how polar a bond is in a molecule. It is calculated as the product of the charge or the partial charge of the atoms and the distance between them (μ = q × d). In other words, a larger dipole moment means a higher polarity in a molecule and vice-versa.

Electronegativity of involved elements

In order to understand the variations among the chlorinated derivatives of methane, we need to first consider the electronegativities of hydrogen (H), carbon (C), and chlorine (Cl) atoms. Electronegativity is the ability of an atom to attract the shared electrons in a covalent bond. Hydrogen is the least electronegative atom of all with a value of 2.1, carbon holds a value of 2.5, and chlorine's value is 3.0. Higher electronegativities indicate a greater pull on the shared electrons, which can lead to higher dipole moments.

Chlorinated derivatives of methane

We will look into the chlorinated derivatives of methane one by one: 1. Chloromethane (CH3Cl) 2. Dichloromethane (CH2Cl2) 3. Trichloromethane (CHCl3) 4. Tetrachloromethane (CCl4 -- also known as carbon tetrachloride)

Dipole moment of chloromethane (CH3Cl)

Chloromethane (CH3Cl) has a tetrahedral geometry, with hydrogen atoms and one chlorine atom surrounding the carbon atom. Due to the larger electronegativity of the chlorine atom, the C-Cl bond becomes quite polar, generating a significant dipole moment.

Dipole moment of dichloromethane (CH2Cl2) and trichloromethane (CHCl3)

As we replace more hydrogen atoms with chlorine, the resultant molecule becomes more symmetrical in nature. For instance, in dichloromethane (CH2Cl2), even though there are two polar C-Cl bonds, the dipole moments of those bonds partially cancel each other out due to the symmetrical shape of the molecule. Trichloromethane (CHCl3) faces the same effect - three C-Cl bond dipoles partially cancel each other, leading to a smaller overall dipole moment.

Dipole moment of tetrachloromethane (CCl4)

In the case of tetrachloromethane (CCl4), the molecule is completely symmetric, thus the dipoles associated with each of the C-Cl bonds cancel each other out entirely, resulting in no net dipole moment. This is why tetrachloromethane has the smallest dipole moment among the chlorinated derivatives of methane. In summary, chloromethane has the largest dipole moment because of the highly polar C-Cl bond, while the dipole moment decreases in the other chlorinated derivatives due to the increasing symmetry of the molecules. Tetrachloromethane has the smallest dipole moment because its completely symmetric structure results in a net dipole moment of zero.