Final answer:
Molecules are ordered by increasing polarity based on their electron density and electronegativity differences. CF4 and CH4 are nonpolar; replacing hydrogen with fluorine in CH3F, CH2F2, and CHF3 increases polarity, with CHF3 being the most polar.
Step-by-step explanation:
To place the molecules CH₄, CH₃F, CH₂F₂, CHF₃, and CF₄ in order of increasing polarity, one must consider the distribution of electron density and the electronegativities of the atoms involved. The more fluorine atoms there are, the polar the molecule generally becomes, as fluorine is highly electronegative (with an electronegativity of 4.0). This difference in electronegativity between carbon and fluorine will lead to an uneven distribution of electrons, creating dipoles across the covalent bonds.
Using electrostatic potential maps and electron density surfaces, we can visualize this concept. Molecules with low electron density (blue areas) are relatively positive, while high electron density areas (red areas) are relatively negative. Based on this principle, the molecules would be arranged in order of increasing polarity as:
- CF₄ (nonpolar)
- CH₄ (nonpolar)
- CH₃F (polar)
- CH₂F₂ (more polar)
- CHF₃ (most polar)
CF₄ and CH₄ are nonpolar molecules due to their symmetry. As we substitute hydrogen atoms with fluorine atoms, the electronegativity difference increases, the electron density shifts towards fluorine, and the molecular polarity increases. Hence, CH₃F, CH₂F₂, and CHF₃ show increasing polarity due to the increasing presence of the electronegative fluorine atoms, which creates stronger dipoles within the molecules.