Which pair of molecules has the strongest dipole-dipole interactions?

a- CO2 and CO2
b- CO2 and CH4
c- NH3 and NH3
d- NH3 and CH4
e- CH4 and CH4

how do you figure out the answer to this question?

1. You know what makes a dipole.

2. You review to see which has two dipoles.

Symmetry is a big clue in this. CO2 are linear molecules, CH4 is a symmetrical (tetrahedral) molecule, and NH3 is not symmetrical, with a double unshared pair of electrons on one side.

To determine which pair of molecules has the strongest dipole-dipole interactions, we need to examine the polarity of each molecule. Dipole-dipole interactions occur between polar molecules that have a positive and negative end.

a) CO2 and CO2: Carbon dioxide (CO2) is a linear molecule with two polar bonds, but the polar bonds cancel each other out due to the arrangement of the atoms. As a result, CO2 is a nonpolar molecule, and it does not have dipole-dipole interactions.

b) CO2 and CH4: Carbon dioxide (CO2) is a nonpolar molecule, as mentioned above. Methane (CH4) is also a nonpolar molecule because the carbon-hydrogen bonds are nonpolar. Therefore, this pair does not have dipole-dipole interactions.

c) NH3 and NH3: Ammonia (NH3) is a pyramidal molecule with a lone pair of electrons on the nitrogen atom. The nitrogen-hydrogen bonds are polar, resulting in a net molecular dipole moment. Hence, NH3 is a polar molecule capable of dipole-dipole interactions. Pairing it with another NH3 molecule will result in the strongest dipole-dipole interactions.

d) NH3 and CH4: Ammonia (NH3) is a polar molecule, as explained earlier. Methane (CH4) is a nonpolar molecule, as all the carbon-hydrogen bonds are nonpolar. Thus, this pair does not have strong dipole-dipole interactions.

e) CH4 and CH4: Methane (CH4) is a nonpolar molecule because the carbon-hydrogen bonds are nonpolar. Therefore, this pair does not have dipole-dipole interactions.

Based on the information provided above, the pair of molecules with the strongest dipole-dipole interactions is option c- NH3 and NH3.

To determine which pair of molecules has the strongest dipole-dipole interactions, you need to consider the polarity of the molecules. Dipole-dipole interactions occur between the positive end of one molecule and the negative end of another molecule. The strength of these interactions depends on the magnitude of the dipole moments present in the molecules.

To figure out the answer, you need to know the molecular geometry and the electronegativity of the atoms within each molecule. Here are the steps to take:

1. Look at each molecule and determine its molecular geometry. This will help identify the polarity of the molecule. For example:
- CO2 has a linear geometry, making it a nonpolar molecule because the dipoles of the two oxygen atoms cancel each other out.
- CH4 has a tetrahedral geometry, making it a nonpolar molecule because the dipoles of the four hydrogen atoms cancel each other out.
- NH3 has a trigonal pyramidal geometry, making it a polar molecule because the dipoles of the three hydrogen atoms do not cancel out.

2. Next, determine the electronegativity difference between the atoms in each molecule. Electronegativity is a measure of an atom's attraction for electrons. A larger electronegativity difference between atoms leads to stronger dipole moments. The values for electronegativity can be found in a periodic table.

3. Compare the electronegativity difference and molecular geometry for each pair of molecules. The pair that has a larger electronegativity difference and a non-cancelled dipole moment (polar molecule) will have the strongest dipole-dipole interactions.

Based on these considerations, the correct answer is: c- NH3 and NH3. Ammonia (NH3) has a trigonal pyramidal geometry and a non-zero dipole moment due to the electronegativity difference between nitrogen and hydrogen.