Question

The molecule shown here is difluoromethane \(\left(\mathrm{CH}_{2} \mathrm{~F}_{2}\right)\), which is used as a refrigerant called \(R-32\). (a) Based on the structure, how many electron domains surround the \(\mathrm{C}\) atom in this molecule? (b) Would the molecule have a nonzero dipole moment? (c) If the molecule is polar, which of the following describes the direction of the overall dipole moment vector in the molecule: (i) from the carbon atom toward a fluorine atom, (ii) from the carbon atom to a point midway between the fluorine atoms, (iii) from the carbon atom to a point midway between the hydrogen atoms, or (iv) From the carbon atom toward a hydrogen atom? [Sections \(9.2\) and 9.3]

Short answer

(a) There are 4 electron domains surrounding the carbon atom in difluoromethane (CH2F2). (b) Yes, the molecule has a nonzero dipole moment due to non-cancellation of polar C-F and C-H bonds in the tetrahedral geometry. (c) The direction of the overall dipole moment vector in the molecule is (i) from the carbon atom toward a fluorine atom.

Step-by-step solution

Identify the structure of the molecule

Draw the Lewis structure of difluoromethane (CH2F2). Carbon has 4 valence electrons, hydrogen has 1, and fluorine has 7. C: 1 H-H bond and 2 C-F bonds H: 1 H-C bond F: 1 C-F bond The structure would look like: H | H--C--F | F

Determine electron domains surrounding the carbon atom

In order to find the electron domains surrounding the carbon atom, we need to count the bonding and non-bonding electron pairs around the carbon. In the case of CH2F2, carbon has four bonding electron pairs (two with hydrogen and two with fluorine). Therefore, there are 4 electron domains surrounding the carbon atom.

Determine if the molecule has a nonzero dipole moment

A nonzero dipole moment occurs when there is an uneven distribution of electron density in a molecule and bonds exhibit polarity, creating a positive and a negative end. In CH2F2, there are polar C-F bonds due to the difference in electronegativity between carbon and fluorine. However, the arrangement of these bonds can either enhance or cancel out the overall dipole moment. Since the molecular geometry is tetrahedral, the dipole vectors of the two C-F bonds and those of the two C-H bonds don't cancel each other out. Hence, the molecule has a nonzero dipole moment.

Determine the direction of the overall dipole moment vector

The overall dipole moment vector points toward the more electronegative element in the molecule. In this case, fluorine is the most electronegative element. Here, we have the given options: (i) from the carbon atom toward a fluorine atom (ii) from the carbon atom to a point midway between the fluorine atoms (iii) from the carbon atom to a point midway between the hydrogen atoms (iv) from the carbon atom toward a hydrogen atom Since the dipole moment vector points towards the more electronegative element, the direction of the overall dipole moment vector in the molecule is (i) from the carbon atom toward a fluorine atom.

Key concepts

Electron Domains

In molecular chemistry, electron domains refer to regions around a central atom where electrons are likely to be found. These regions include both bonding electron pairs (shared with neighboring atoms forming a bond) and non-bonding electron pairs (lone pairs).