Final answer:
Among the choices, HF and CN- contain covalent bonds. HF has a polar covalent bond due to the electronegativity difference between hydrogen and fluorine. CN- features a covalent bond since carbon and nitrogen have similar electronegativities. So the correct options are A and C.
Step-by-step explanation:
The subject of this question is identifying which of the given molecules contains a covalent bond. To determine the type of bond, we look at the difference in electronegativity between the bonded atoms. A covalent bond is formed when two atoms share electrons, typically occurring between nonmetal atoms with similar electronegativities. When the electronegativity difference is small, the bond is most definitely covalent.
Given the options:
- HF: The bond between hydrogen (H) and fluorine (F) is a polar covalent bond, due to the significant, but not excessively large, difference in electronegativity (1.9 according to provided information).
- LiCl: Lithium (Li) and chlorine (Cl) form an ionic bond due to the large electronegativity difference (more than 1.7).
- CN-: The carbon (C) and nitrogen (N) in the cyanide ion have similar electronegativities and share electrons, indicating a covalent bonding.
- MgO: Magnesium (Mg) and oxygen (O) form an ionic bond due to the very high difference in electronegativities.
Therefore, the molecules containing covalent bonds are HF and CN-. HF contains a polar covalent bond, and CN- contains a covalent bond within its structure.