π Covalent bonds sharing electrons (10 MCQs)
π From Campbell Biology β’ 2. The Chemistry of Life β’ 10 questions available
What is Covalent bonds sharing electrons?
Definition:
Covalent bonds are chemical bonds where atoms share one or more pairs of electrons to achieve a stable electron configuration, typically a full outer shell, and they are common in organic molecules and biological macromolecules, with the strength of the bond determined by the number of shared electron pairs (single, double, or triple bonds) and the distance between nuclei, and they can be polar or nonpolar depending on the electronegativity of the atoms involved.
Working:
Covalent bonds work by overlapping atomic orbitals, allowing electrons to be shared, and the bond energy is the energy required to break the bond, with the equation ; in a nonpolar covalent bond (e.g., H-H), electrons are shared equally, while in a polar covalent bond (e.g., H-O), electrons are shared unequally due to electronegativity differences, creating partial charges; covalent bonds are directional, giving molecules specific shapes, and they are the primary bonds in organic and biochemical compounds.
Example:
A simple example is the bond between two hydrogen atoms (Hβ), where each atom shares one electron, forming a single covalent bond and achieving the stable helium configuration; another example is the double bond in oxygen (Oβ), where two atoms share two pairs of electrons, illustrating how covalent bonds form stable molecules that are essential for life.
Reason:
Covalent bonds are the foundation of organic chemistry and biochemistry, as they form the backbone of all biomolecules, and understanding them is essential for explaining molecular structure, enzyme catalysis, and drug-receptor interactions.
π All Covalent bonds sharing electrons MCQs
Q1. Two atoms each have one unpaired electron in their outermost regions. They approach closely and form a stable molecule. Which model best explains the stability gained during bonding?
π Explanation: A covalent bond forms when atoms share electron pairs, allowing each atom to reach a lower-energy and generally more stable electron arrangement. The shared electrons are attracted to both nuclei, helping hold the atoms together.
Q2. A student claims, "Any two atoms that share electrons must form a nonpolar covalent bond." Which evaluation is most accurate?
π Explanation: Electron sharing does not necessarily mean equal sharing. If bonded atoms have different abilities to attract shared electrons, the electron density becomes uneven, producing a polar covalent bond with partial charges.
Q3. Consider two bonds: Bond X has nearly equal electron sharing, while Bond Y has strongly unequal sharing. If the bonded atoms in both cases are similar in size, which conclusion is most reasonable?
π Explanation: Unequal sharing creates partial charges because electron density is pulled closer to one atom. Therefore, Bond Y would have a stronger separation of charge, whereas nearly equal sharing in Bond X produces little or no bond polarity.
Q4. A molecule contains two identical atoms connected by a covalent bond. A model predicts that one atom becomes slightly positive and the other slightly negative. What is the best criticism of the model?
π Explanation: Identical atoms have the same tendency to attract the shared electron pair. Consequently, the electron density should be distributed symmetrically rather than producing a permanent partial positive charge on one atom.
Q5. A chemist compares two molecules. In Molecule P, the central atom forms four single covalent bonds. In Molecule Q, the central atom forms two single bonds and one double bond. Which statement best compares the bonding models?
π Explanation: A single covalent bond represents one shared electron pair, while a double covalent bond represents two shared pairs. Thus, the double bond contributes greater shared electron density between the bonded atoms.
Q6. A molecule is designed with one atom that strongly attracts shared electrons and another that weakly attracts them. As the atoms approach, which sequence best describes the expected outcome?
π Explanation: When one bonded atom attracts the shared electrons more strongly, electron density shifts toward that atom. This creates partial negative and positive regions rather than complete electron transfer, characteristic of polar covalent bonding.
Q7. A student draws a covalent bond but places both shared electrons entirely around only one atom while still labeling the bond nonpolar. What is the main error?
π Explanation: A nonpolar covalent bond involves approximately equal sharing of the bonding electrons. Concentrating both electrons around one atom represents highly unequal sharing and therefore conflicts with the proposed nonpolar model.
Q8. A graph shows bond polarity on the vertical axis and difference in electron-attracting ability between bonded atoms on the horizontal axis. The curve rises steadily as the difference increases. Which interpretation is best supported by the graph?
π Explanation: The graph indicates a positive relationship between the difference in electron-attracting ability and bond polarity. As the difference grows, shared electrons are distributed more unevenly, increasing partial-charge separation.
Q9. A molecule contains several covalent bonds. Individually, some bonds are polar, but the molecule as a whole has no net dipole. Which explanation best accounts for this observation?
π Explanation: Molecular polarity depends on both individual bond polarities and their three-dimensional arrangement. Polar bond dipoles can point in opposing directions and cancel, producing a molecule with no overall dipole despite containing polar bonds.
Q10. Two hypothetical bonds have identical bond lengths. Bond A shares one electron pair, while Bond B shares two electron pairs between the same atoms. If all other conditions are comparable, which prediction is most defensible?
π Explanation: A single bond contains one shared electron pair, whereas a double bond contains two shared pairs. Greater shared electron density between the nuclei generally strengthens the interaction, although actual bond strength also depends on atomic identity and molecular structure.