Question

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

Short answer

The hydrides and their type are: a. \(\mathrm{BaH}_2\): Ionic hydride b. \(\mathrm{H}_2\mathrm{Te}\): Molecular hydride c. \(\mathrm{TiH}_{1.7}\): Metallic hydride

Step-by-step solution

Analyze the elements in each compound

We need to understand the elements involved in the compounds to identify the type of hydride. Let's analyze the elements present in each compound. a. In \(\mathrm{BaH}_2\), \(\mathrm{Ba}\) is a metal (Barium), from group 2 in the periodic table, and \(\mathrm{H}\) is Hydrogen. b. In \(\mathrm{H}_2\mathrm{Te}\), \(\mathrm{Te}\) is a nonmetal (Tellurium), from group 16 in the periodic table, and \(\mathrm{H}\) is Hydrogen. c. In \(\mathrm{TiH}_{1.7}\), \(\mathrm{Ti}\) is a transition metal (Titanium), from group 4 in the periodic table, and \(\mathrm{H}\) is Hydrogen.

Identify the type of hydride for each compound

Now we can use the general characteristics of each type of hydride to identify the type of hydride for each compound. a. \(\mathrm{BaH}_2\): Since Barium is a metal and it bonds with Hydrogen, we conclude that this hydride is ionic. b. \(\mathrm{H}_2\mathrm{Te}\): Since Tellurium is a nonmetal and it bonds with Hydrogen, we conclude that this hydride is molecular. c. \(\mathrm{TiH}_{1.7}\): Since Titanium is a transition metal and it bonds with Hydrogen, we conclude that this hydride is metallic. So, the hydrides and their type are: a. \(\mathrm{BaH}_2\): Ionic hydride b. \(\mathrm{H}_2\mathrm{Te}\): Molecular hydride c. \(\mathrm{TiH}_{1.7}\): Metallic hydride

Key concepts

Ionic Hydrides

Ionic hydrides, also known as saline hydrides, are formed when hydrogen bonds with alkali or alkaline earth metals. This type of bonding typically occurs with elements from Groups 1 and 2 of the periodic table, like Sodium (Na) and Barium (Ba). For example, in the compound \( \text{BaH}_2 \), we find an ionic hydride because Barium (Ba), a metal from Group 2, forms ionic bonds with hydrogen.
The defining characteristic of ionic hydrides is the transfer of electrons. When the metal atom loses its valence electron(s) to hydrogen, it results in a cation of the metal and a hydride anion (\( \text{H}^- \)). This gives ionic hydrides their specific properties, such as high melting and boiling points.
- **Key Properties of Ionic Hydrides**:

• Typically crystalline solids
• High melting and boiling points due to strong ionic bonds
• Conduct electricity in molten state
• Reacts with water to produce hydrogen gas

Molecular Hydrides

Molecular hydrides, or covalent hydrides, occur when hydrogen forms bonds with nonmetals. These hydrides are a result of the sharing of electrons between hydrogen and another nonmetal element, leading to the formation of a covalent bond. This can be seen in compounds like \( \text{H}_2\text{Te} \), where Tellurium (Te) belongs to the nonmetals in Group 16.
Molecular hydrides exhibit significant variability depending on the involved nonmetals, which makes them quite versatile. For instance, these hydrides can exist as gases, liquids, or solids at room temperature. This variation is due to the weaker intermolecular forces, such as Van der Waals forces or hydrogen bonds, that hold molecules together in these compounds, unlike the strong ionic bonds in ionic hydrides.
- **Key Features of Molecular Hydrides**:

• Can exist in various states (solid, liquid, gas)
• Generally have low melting and boiling points
• Non-electrolytic in nature
• Often are volatile compounds

Metallic Hydrides

Metallic hydrides, also known as interstitial hydrides, are typically formed when transition metals absorb hydrogen. In these hydrides, hydrogen atoms occupy the interstitial spaces (gaps) in the metallic lattice. Compounds like \( \text{TiH}_{1.7} \) fall under this category, with Titanium (Ti) being a transition metal absorbing hydrogen.
The formation of metallic hydrides involves little effect on the metallic bonding of the parent metal, allowing these hydrides to retain a metallic character. They are often non-stoichiometric, meaning the ratio of hydrogen to metal atoms can vary (as seen in the subscript 1.7 in \( \text{TiH}_{1.7} \)). This characteristic allows metallic hydrides to play significant roles in hydrogen storage technology.
- **Characteristics of Metallic Hydrides**:

• Possess metal-like properties, such as electrical conductivity
• Often tough and brittle
• Have variable hydrogen to metal ratios
• Potential use in hydrogen storage solutions due to capacity to reversibly absorb and release hydrogen