In which of the following substances are the atoms held together by polar covalent bonds?

• A. O2
• B. CH4
• C. NaCl
• D. HCl

Answer: (D)

Verified step by step guidance

1. Understand the types of chemical bonds: ionic bonds form between metals and nonmetals with large differences in electronegativity, covalent bonds form between nonmetals sharing electrons, and polar covalent bonds occur when electrons are shared unequally due to differences in electronegativity between the atoms.
2. Analyze each substance's bonding: O\_2 consists of two identical oxygen atoms sharing electrons equally, so the bond is nonpolar covalent.
3. CH\_4 (methane) has carbon and hydrogen atoms; since the electronegativity difference is small, the bonds are considered nonpolar covalent.
4. NaCl is composed of sodium (a metal) and chlorine (a nonmetal), so the bond is ionic due to the large electronegativity difference and electron transfer.
5. HCl consists of hydrogen and chlorine atoms; chlorine is more electronegative than hydrogen, causing an unequal sharing of electrons, which results in a polar covalent bond.