For each of the following pairs of molecules, determine which is most polar:
C2H4 or C2H5OH
C2H6 or CH3OCH3
CCl4 or CF4
H2O or HsS
Question 8 options:
a) C2H4 , C2H6 , CF4, HsS
b) C2H5OH, CH3OCH3, CCl4, HsS
c) C2H5OH, CH3OCH3, CF4, HsS
d) C2H4, C2H6, CF4, H2O
e) C2H5OH, CH3OCH3, CF4, H2O
The most polar molecule in each pair is the one that has a greater electronegativity difference between the atoms. This means that the atom with the higher electronegativity will have a greater pull on the shared electrons, resulting in a more polar bond.
a) C2H4 or C2H5OH
C2H4: This molecule is nonpolar because there is no significant electronegativity difference between carbon and hydrogen.
C2H5OH: This molecule is polar because there is a significant electronegativity difference between carbon and oxygen in the alcohol functional group.
b) C2H6 or CH3OCH3
C2H6: This molecule is nonpolar because there is no significant electronegativity difference between carbon and hydrogen.
CH3OCH3: This molecule is polar because there is a significant electronegativity difference between carbon and oxygen in the ether functional group.
c) CCl4 or CF4
CCl4: This molecule is nonpolar because there is no significant electronegativity difference between carbon and chlorine.
CF4: This molecule is polar because fluorine is more electronegative than carbon, resulting in a polar bond.
d) H2O or H2S
H2O: This molecule is highly polar because there is a significant electronegativity difference between oxygen and hydrogen.
H2S: This molecule is less polar than H2O because there is a smaller electronegativity difference between sulfur and hydrogen.
Comparing the most polar molecules from each pair, we can see that the answer is:
e) C2H5OH, CH3OCH3, CF4, H2O
To determine which molecule is most polar, we need to consider the electronegativity difference between the atoms in the molecule.
The electronegativity difference is the measure of the tendency of an atom to attract electrons towards itself in a chemical bond. The greater the electronegativity difference between two atoms, the more polar the bond between them and the overall molecule.
In the case of the given molecules:
1) C2H4 or C2H5OH:
- In C2H4 (ethene), carbon is bonded to carbon using a double bond, and both carbon atoms have the same electronegativity, so the bond is nonpolar.
- In C2H5OH (ethanol), there is an oxygen atom bonded to a carbon atom, and the oxygen atom is more electronegative than carbon. This creates a polar bond between the carbon and oxygen, making the molecule polar overall. Therefore, C2H5OH (ethanol) is the more polar molecule.
2) C2H6 or CH3OCH3:
- In C2H6 (ethane), all the carbon-hydrogen bonds have similar electronegativities, resulting in nonpolar C-H bonds. The molecule is nonpolar.
- In CH3OCH3 (dimethyl ether), there is an oxygen atom bonded to two carbon atoms. The oxygen atom is more electronegative than carbon, leading to polar bonds between carbon and oxygen. This makes CH3OCH3 (dimethyl ether) the more polar molecule.
3) CCl4 or CF4:
- Both CCl4 (carbon tetrachloride) and CF4 (carbon tetrafluoride) have similar molecular structures, with four identical bonds to carbon. Chlorine and fluorine are both highly electronegative atoms.
- While CCl4 has polar C-Cl bonds, CF4 has polar C-F bonds. However, in CCl4, the polarities of all the C-Cl bonds cancel each other out due to the symmetrical arrangement of the chlorine atoms around the central carbon atom. Therefore, CCl4 is a nonpolar molecule.
- In CF4, the symmetrical arrangement also exists, but the fluorine atoms are more electronegative than the chlorine atoms, resulting in more polar C-F bonds. Thus, CF4 is a polar molecule.
4) H2O or H2S:
- In H2O (water), there is an oxygen atom bonded to two hydrogen atoms. Oxygen is more electronegative than hydrogen, creating polar O-H bonds.
- In H2S (hydrogen sulfide), there is a sulfur atom bonded to two hydrogen atoms. Sulfur is also more electronegative than hydrogen, creating polar S-H bonds.
- However, oxygen is more electronegative than sulfur, resulting in a greater electronegativity difference in H2O (water) compared to H2S (hydrogen sulfide). Thus, H2O is the more polar molecule.
Based on these explanations, the correct answer is option d) C2H4, C2H6, CF4, H2O.
To determine which molecule is more polar in each pair, we need to consider the electronegativity of the atoms involved.
1. C2H4 or C2H5OH:
- C2H4 is an alkene, containing only carbon and hydrogen atoms. Both atoms have similar electronegativities, so the molecule is nonpolar.
- C2H5OH is ethanol, which contains an oxygen atom. Oxygen is more electronegative than carbon and hydrogen, causing a polar covalent bond between oxygen and hydrogen. Therefore, C2H5OH is more polar than C2H4.
2. C2H6 or CH3OCH3:
- C2H6 is an alkane, consisting only of carbon and hydrogen atoms. Again, the electronegativities of carbon and hydrogen are similar, making the molecule nonpolar.
- CH3OCH3 is dimethyl ether, which contains an oxygen atom. Similar to the previous case, the presence of oxygen results in a polar covalent bond between oxygen and hydrogen. Hence, CH3OCH3 is more polar than C2H6.
3. CCl4 or CF4:
- Both CCl4 and CF4 contain a central carbon atom surrounded by four halogen atoms (chlorine or fluorine). However, fluorine is more electronegative than chlorine. Thus, the C-F bonds in CF4 are more polar than the C-Cl bonds in CCl4. Hence, CF4 is more polar than CCl4.
4. H2O or HsS:
- H2O is water, and HsS is hydrogen sulfide. Both molecules contain oxygen and sulfur atoms, but oxygen is more electronegative than sulfur. Therefore, the O-H bonds in H2O are more polar than the S-H bonds in HsS. Consequently, H2O is more polar than HsS.
Combining the analyses of each pair, we can see that the correct option is:
c) C2H5OH, CH3OCH3, CF4, HsS