Chemistry Practice Test: Ionic and Covalent Bonding

Calcium is a metal that easily loses electrons and chlorine is a nonmetal that easily gains them, so electrons are transferred. The other three pairs are all nonmetals, which share electrons in covalent bonds.

Three Mg²⁺ ions (+6) balance two N³⁻ ions (−6), giving Mg₃N₂. Mg₂N₃ puts the subscripts the wrong way round and has a total charge of −5.

Calcium becomes Ca²⁺ by losing two electrons, and each chlorine atom gains one to become Cl⁻. Sharing electron pairs describes covalent bonding, not the ionic bonds in CaCl₂.

Each double bond is two shared pairs, and there are two double bonds, so 4 pairs (8 electrons) are shared. The answer 8 counts shared electrons instead of shared pairs.

Oxygen is more electronegative, so it pulls the shared pair closer and gets a partial negative charge, making the bond polar covalent. A difference of 1.4 is not large enough for the electrons to be fully transferred.

Sugar is made of neutral molecules held by weak forces, so it melts at a low temperature and does not form ions in water. Conducting in solution is a property of ionic compounds such as salt.

Sodium chloride is made of ions in both states, but current needs charged particles that can move. Melting frees the ions; it does not turn molecules into ions.

The attraction between ions grows with their charges, and 2+ with 2− is much stronger than 1+ with 1−. MgO is an ionic compound, and its formula mass (40) is actually smaller than that of NaCl (58.5).

More shared pairs pull the two nuclei closer together and hold them more tightly, so a triple bond is shorter and stronger than a double or single bond. The single bond in ethane is the longest and weakest.

The nitrate ion is a group of atoms held together by shared electrons, and the whole ion is attracted to Na⁺ by an ionic bond. Compounds with polyatomic ions contain both bond types.