Answer:
Step-by-step explanation:
Dipole-dipole interactions occur between polar molecules and result from the attraction between the positive end of one molecule and the negative end of another molecule. To determine which molecule is likely to have the most significant contribution from dipole-dipole interactions, we need to consider the polarity of each molecule.
1. H₂O:
Water (H₂O) is a polar molecule due to its bent molecular geometry and the presence of electronegative oxygen and hydrogen atoms. The oxygen atom is more electronegative than the hydrogen atoms, resulting in a partial negative charge on the oxygen and partial positive charges on the hydrogens. Dipole-dipole interactions are likely to make a significant contribution to the intermolecular forces in water.
2. SF₆:
Sulfur hexafluoride (SF₆) is a nonpolar molecule. It consists of six fluorine atoms surrounding a central sulfur atom, arranged symmetrically in an octahedral shape. The bond dipoles cancel each other out, resulting in a molecule with no net dipole moment. Therefore, dipole-dipole interactions are not likely to contribute significantly to the intermolecular forces in SF₆.
3. CH₃Cl:
Chloromethane (CH₃Cl) is a polar molecule. The chlorine atom is more electronegative than the carbon and hydrogen atoms, resulting in a partial negative charge on the chlorine and partial positive charges on the carbon and hydrogens. Dipole-dipole interactions are likely to make a significant contribution to the intermolecular forces in CH₃Cl.
4. NH₃:
Ammonia (NH₃) is a polar molecule. The nitrogen atom is more electronegative than the hydrogen atoms, resulting in a partial negative charge on the nitrogen and partial positive charges on the hydrogens. Dipole-dipole interactions are likely to make a significant contribution to the intermolecular forces in NH₃.
5. BH₃:
Boron trihydride (BH₃) is a nonpolar molecule. It consists of three hydrogen atoms bonded to a central boron atom, arranged in a trigonal planar shape. The bond dipoles cancel each other out, resulting in a molecule with no net dipole moment. Therefore, dipole-dipole interactions are not likely to contribute significantly to the intermolecular forces in BH₃.
6. C₈H₁₇Br:
Octyl bromide (C₈H₁₇Br) is a nonpolar molecule. The carbon-bromine bond is polar due to the difference in electronegativity between carbon and bromine. However, the long carbon chain in the molecule results in a symmetrical distribution of partial charges, canceling out the overall dipole moment. Therefore, dipole-dipole interactions are not likely to contribute significantly to the intermolecular forces in C₈H₁₇Br.
In summary, the molecules in which dipole-dipole interactions are likely to make the most significant contribution to intermolecular forces are:
1. H₂O (water)
3. CH₃Cl (chloromethane)
4. NH₃ (ammonia)
These molecules have polar bonds and a net dipole moment, making them susceptible to dipole-dipole interactions.