Problem 27 - Chemistry The Central Science

Question

Identify the following hydrides as ionic, metallic, or molecular: (a) \(\mathrm{BaH}_{2},\) (b) \(\mathrm{H}_{2} \mathrm{Te},\) (c) \(\mathrm{TiH}_{1.7}\).

Step-by-Step Solution

Answer

The hydrides can be classified as follows: (a) \(\mathrm{BaH}_{2}\) is an ionic hydride, (b) \(\mathrm{H}_{2}\mathrm{Te}\) is a molecular (covalent) hydride, and (c) \(\mathrm{TiH}_{1.7}\) is a metallic hydride.

Step 1: Identify the Element in Each Hydride

For this exercise, we'll be focusing on the different elements present in each given hydride: (a) \(\mathrm{BaH}_{2}\) - Barium (Ba) from Group 2 (b) \(\mathrm{H}_{2}\mathrm{Te}\) - Tellurium (Te) from Group 16 (c) \(\mathrm{TiH}_{1.7}\) - Titanium (Ti) from the transition metal group

Step 2: Determine Hydride Type#a) - Barium Hydride

Barium is an alkaline earth metal in group 2, which typically forms ionic hydrides. As a result, Barium hydride \(\mathrm{BaH}_{2}\) can be classified as an ionic hydride.

Step 3: Determine Hydride Type#b) - Hydrogen Telluride

Tellurium is a non-metal in group 16, so it forms molecular (covalent) hydrides with hydrogen. Thus, Hydrogen Telluride \(\mathrm{H}_{2}\mathrm{Te}\) can be classified as a molecular hydride.

Step 4: Determine Hydride Type#c) - Titanium Hydride

Titanium is a transition metal, which generally forms metallic hydrides. Therefore, Titanium hydride \(\mathrm{TiH}_{1.7}\) can be classified as a metallic hydride.

Step 5: In Summary

Using the categories outlined above, the types of hydrides are as follows: (a) \(\mathrm{BaH}_{2}\) - Ionic Hydride (b) \(\mathrm{H}_{2}\mathrm{Te}\) - Molecular (covalent) Hydride (c) \(\mathrm{TiH}_{1.7}\) - Metallic Hydride

Key Concepts

Ionic Hydrides

Ionic hydrides form when hydrogen bonds with highly electropositive elements, primarily the alkali and alkaline earth metals. These metals are in Groups 1 and 2 of the periodic table. Ionic hydrides are created through the transfer of electrons from the metal to hydrogen, resulting in the formation of hydride ions (H⁻). This makes them characteristically ionic in nature.

• Characteristics: Ionic hydrides are usually white crystalline solids and have high melting and boiling points.
• Reactivity: They can react with water to produce hydrogen gas and a base. For example, barium hydride (BaH₂) reacts vigorously with water.
• Example: BaH₂ is a classic ionic hydride where barium donates electrons to form H⁻ ions.

Molecular Hydrides

Molecular hydrides are formed when hydrogen bonds with non-metals, typically those in groups 14 through 16 of the periodic table. These hydrides consist of covalent bonds, which means the sharing of electrons between the hydrogen and the non-metal atoms.

• Characteristics: They are often found as gases or liquids at room temperature. They have relatively low melting and boiling points compared to ionic hydrides.
• Common Examples: Water (H₂O), methane (CH₄), and hydrogen telluride (H₂Te) are well-known molecular hydrides.
• Hydrogen Telluride: H₂Te, with tellurium from group 16, forms a molecular hydride due to its covalent bonding.

Metallic Hydrides

Metallic hydrides are formed when hydrogen interacts with d-block or f-block elements, typically transition metals or rare earth metals. Unlike ionic and molecular hydrides, metallic hydrides possess a more complex structure where hydrogen atoms occupy interstitial sites in the metal lattice.

• Characteristics: They often display metallic characteristics such as electrical conductivity and luster.
• Composition Variability: These hydrides often have non-stoichiometric compositions because the number of hydrogen atoms can vary. For example, TiH₁.₇ shows variable hydrogen content.
• Titanium Hydride: TiH₁.₇ is a great example of a metallic hydride where titanium, a transition metal, integrates hydrogen into its lattice.