Which of the statements below best describes polar covalent bonds?
A) The sharing of a hydrogen atom between two molecules.
B) The complete transfer of an electron from one atom to another; relatively weak bond.
C) The complete transfer of an electron from one atom to another; relatively strong bond.
D) The sharing of an electron pair between two atoms in which the less electronegative atom spends significantly more time close to the electron pair.
E) The sharing of an electron pair between two atoms in which the more electronegative atom spends significantly more time close to the electron pair.
The correct answer and explanation is:
The correct answer is E) The sharing of an electron pair between two atoms in which the more electronegative atom spends significantly more time close to the electron pair.
Polar covalent bonds occur when two atoms share an electron pair, but the sharing is not equal. This happens due to differences in electronegativity between the two atoms involved. Electronegativity is a measure of an atom’s ability to attract and hold onto electrons. In a polar covalent bond, one atom has a higher electronegativity than the other, which means it will attract the shared electrons more strongly. As a result, the electron pair spends more time closer to the more electronegative atom, creating a partial negative charge (δ-) on that atom, and a partial positive charge (δ+) on the less electronegative atom.
This unequal sharing of electrons leads to a dipole in the molecule, where one end of the molecule is slightly negative and the other is slightly positive. An example of a polar covalent bond is the bond between hydrogen and oxygen in a water molecule (H2O), where oxygen is more electronegative than hydrogen and attracts the electron pair more strongly.
Now, let’s review why the other options are incorrect:
- A) The sharing of a hydrogen atom between two molecules refers to a hydrogen bond, which is a type of intermolecular force, not a covalent bond.
- B) The complete transfer of an electron from one atom to another; relatively weak bond describes an ionic bond, not a covalent one.
- C) The complete transfer of an electron from one atom to another; relatively strong bond also describes an ionic bond, which typically forms between atoms with a large difference in electronegativity.
- D) The sharing of an electron pair between two atoms in which the less electronegative atom spends significantly more time close to the electron pair would suggest a bond similar to that in option E, but this is less accurate, as the electron pair would typically be closer to the more electronegative atom.
Thus, option E correctly defines polar covalent bonding.