chemistry : class11 Asymmetrical Bond Polarity : Polar character of covalent bond : Chemical Bonding and Molecular Structure MCQ Questions and Answers
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Asymmetrical Bond Polarity
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MCQ Questions
1. In which bond is the asymmetrical distribution of shared electrons expected to be greatest, assuming the following Pauling electronegativities: C = 2.5, N = 3.0, O = 3.5, F = 4.0?
A.
C–N
B.
N–O
C.
C–O
D.
C–F
Correct Answer:
C–F
Explanation:
Bond polarity increases with the electronegativity difference between the bonded atoms. The differences are 0.5 for C–N, 0.5 for N–O, 1.0 for C–O, and 1.5 for C–F; therefore, C–F has the greatest asymmetrical electron distribution.
2. For the hydrogen halides HF, HCl, HBr, and HI, which bond has the smallest asymmetry in its shared electron pair, using approximate electronegativities H = 2.1, F = 4.0, Cl = 3.0, Br = 2.8, and I = 2.5?
A.
H–F
B.
H–Cl
C.
H–Br
D.
H–I
Correct Answer:
H–I
Explanation:
The electronegativity differences are 1.9 for H–F, 0.9 for H–Cl, 0.7 for H–Br, and 0.4 for H–I. Hence, H–I has the least asymmetrical sharing and the smallest bond polarity among the four.
3. In a polar covalent C–F bond, which statement correctly describes the partial charges produced by asymmetrical sharing of electrons?
A.
Carbon becomes partially negative and fluorine partially positive
B.
Carbon and fluorine acquire equal full charges
C.
Carbon becomes partially positive and fluorine partially negative
D.
Both carbon and fluorine become partially negative
Correct Answer:
Carbon becomes partially positive and fluorine partially negative
Explanation:
Fluorine is more electronegative than carbon and attracts the shared electron pair more strongly. Therefore, fluorine acquires a partial negative charge, while carbon acquires a partial positive charge.
4. Which comparison correctly ranks the polarity of the indicated bonds using electronegativities C = 2.5, H = 2.1, N = 3.0, and O = 3.5?
A.
C–H > C–N > C–O
B.
C–O > C–N > C–H
C.
C–N > C–O > C–H
D.
C–H > C–O > C–N
Correct Answer:
C–O > C–N > C–H
Explanation:
The electronegativity differences are 1.0 for C–O, 0.5 for C–N, and 0.4 for C–H. A larger difference produces greater asymmetry in the covalent electron distribution, giving the order C–O > C–N > C–H.
5. In the bond H–Cl, toward which atom is the bond dipole directed, and why?
A.
Toward H, because hydrogen is smaller
B.
Toward Cl, because chlorine attracts the shared electrons more strongly
C.
Equally toward both atoms, because the bond is covalent
D.
Away from both atoms, because the bond contains no separated charge
Correct Answer:
Toward Cl, because chlorine attracts the shared electrons more strongly
Explanation:
Covalent character does not require equal sharing. Chlorine is more electronegative than hydrogen, so the shared electron density is displaced toward chlorine and the bond dipole points toward the chlorine end.
6. Two bonds, X–Y and X–Z, have electronegativity differences of 0.8 and 1.4, respectively. If their bond lengths and bonding environments are comparable, which bond should possess the larger bond dipole moment?
A.
X–Y, because its atoms are less different in electronegativity
B.
X–Z, because it has greater asymmetry in electron distribution
C.
Both have the same bond dipole because both are covalent
D.
The bond with the smaller atom must always have the larger dipole
Correct Answer:
X–Z, because it has greater asymmetry in electron distribution
Explanation:
A larger electronegativity difference generally produces greater separation of partial charge and therefore a larger bond dipole, provided the bond lengths and environments are comparable. Thus, X–Z is expected to be more polar.
7. Which bond is expected to have its shared electron pair displaced toward the atom written second, based on the electronegativities N = 3.0 and O = 3.5?
A.
O–N
B.
N–O
C.
N–N
D.
O–O
Correct Answer:
N–O
Explanation:
In N–O, oxygen is written second and is more electronegative than nitrogen. Consequently, the shared electron density is displaced toward oxygen, making the bond asymmetrically polar in that direction.
8. Which statement best distinguishes a polar covalent bond from a nonpolar covalent bond in terms of electron sharing?
A.
A polar covalent bond has complete transfer of electrons, whereas a nonpolar bond has partial transfer
B.
A polar covalent bond has unequal sharing caused by different electronegativities, whereas a nonpolar bond has nearly equal sharing
C.
A polar covalent bond always contains a metal, whereas a nonpolar bond contains only nonmetals
D.
A polar covalent bond has no shared electrons, whereas a nonpolar bond has shared electrons
Correct Answer:
A polar covalent bond has unequal sharing caused by different electronegativities, whereas a nonpolar bond has nearly equal sharing
Explanation:
Asymmetrical bond polarity results from unequal attraction of the shared electron pair by the bonded atoms. In a nonpolar covalent bond, the atoms have equal or nearly equal electronegativities, so the sharing is approximately symmetrical.
9. A bond between elements P and Q has P more electronegative than Q. Which notation correctly represents the partial-charge arrangement and the direction of electron-density displacement?
A.
Pδ−–Qδ+, with electron density displaced toward P
B.
Pδ+–Qδ−, with electron density displaced toward P
C.
Pδ−–Qδ−, with electron density displaced equally toward both atoms
D.
Pδ+–Qδ+, with electron density displaced away from P
Correct Answer:
Pδ−–Qδ+, with electron density displaced toward P
Explanation:
Because P is more electronegative, it attracts the shared electron pair more strongly. Electron density shifts toward P, giving P a partial negative charge and Q a partial positive charge.
10. Which change would most directly increase the asymmetrical polarity of a covalent bond between the same two elements?
A.
Replacing one atom with its isotope while keeping the electronic configuration unchanged
B.
Decreasing the electronegativity difference between the two atoms
C.
Increasing the electronegativity difference between the two atoms
D.
Making the bond noncovalent without changing the participating atoms
Correct Answer:
Increasing the electronegativity difference between the two atoms
Explanation:
Greater electronegativity difference causes the bonding electron pair to be attracted more strongly toward one atom. This increases the unequal charge distribution and hence the asymmetrical polarity of the covalent bond.
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