Question

Identify the following hydrides as ionic, metallic, or molecular: (a) \(\mathrm{B}_{2} \mathrm{H}_{6}\), (b) \(\mathrm{RbH}\), (c) \(\mathrm{Th}_{4} \mathrm{H}_{1.5}\)

Short answer

(a) \(\mathrm{B}_{2} \mathrm{H}_{6}\) is a molecular hydride; (b) \(\mathrm{RbH}\) is an ionic hydride; and (c) \(\mathrm{Th}_{4} \mathrm{H}_{1.5}\) is a metallic hydride.

Step-by-step solution

Identify the characteristics of each hydride type

Ionic hydrides: Formed between a highly electropositive metal (Group 1 or Group 2 elements) and hydrogen. These hydrides have ionic bonds due to the difference in electronegativity of metal and hydrogen. Metallic hydrides: Formed between transition, inner transition metals or actinides, and hydrogen. They have metallic bonds and are often non-stoichiometric compounds. Molecular hydrides: Formed between non-metals and hydrogen. They have covalent bonds and are characterized by discrete molecules.

Analyze each given hydride

(a) \(\mathrm{B}_{2} \mathrm{H}_{6}\): Boron is a non-metal, and the compound is composed of boron and hydrogen. The hydride has a well-defined stoichiometry, pointing towards a molecular hydride. (b) \(\mathrm{RbH}\): Rubidium (Rb) is a group 1 metal with low electronegativity, while hydrogen has a relatively high electronegativity. The ionic character of their bond suggests that this hydride is ionic. (c) \(\mathrm{Th}_{4} \mathrm{H}_{1.5}\): Thorium (Th) is an actinide element. Also, the given compound is non-stoichiometric, which is a characteristic of metallic hydrides.

State the type of hydride for each given example

(a) \(\mathrm{B}_{2} \mathrm{H}_{6}\): Molecular hydride (b) \(\mathrm{RbH}\): Ionic hydride (c) \(\mathrm{Th}_{4} \mathrm{H}_{1.5}\): Metallic hydride