Arrange the following molecules from most to least polar and...

Arrange the following molecules from most to least polar and explain your order: $\mathrm{CH}_{4}, \mathrm{CF}_{2} \mathrm{Cl}_{2}, \mathrm{CF}_{2} \mathrm{H}_{2}, \mathrm{CCl}_{4}$, and $\mathrm{CCl}_{2} \mathrm{H}_{2}$.

Key Concepts

Molecular Geometry

Molecular geometry is the three-dimensional arrangement of atoms within a molecule, dictated by electron-pair repulsion and the bonding environment. The shape of a molecule is critical in determining how individual bond dipoles combine; if they are arranged symmetrically, they may cancel out, resulting in a nonpolar molecule despite having polar bonds.

Molecular Symmetry

Molecular symmetry involves the balanced distribution of atoms and groups around a central point or axis. In highly symmetric molecules, even if the bonds themselves are polar, the geometry can lead to cancellation of the bond dipoles, resulting in little or no net molecular dipole moment. Understanding symmetry thus helps in predicting and rationalizing the overall polarity of a molecule.

Dipole Moment

The dipole moment is a quantitative measure of the polarity of a molecule, determined by both the magnitude of the individual bond dipoles and their spatial orientation. It is a vector sum of all the individual bond dipoles, and a net dipole moment indicates that there is an uneven distribution of electron density within the molecule.

Electronegativity

Electronegativity refers to the ability of an atom to attract shared electrons in a chemical bond. The difference in electronegativity between bonded atoms creates polar bonds, with electrons being drawn more towards the more electronegative atom. This concept is essential in understanding why certain bonds are polar, forming the basis for predicting a molecule’s overall polarity.

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