What are metallic or interstitial hydrides? How do they differ from molecular hydrides?

Explanation

**Step-by-Step Solution:**

**Step 1: Define Metallic or Interstitial Hydrides**
Metallic or interstitial hydrides are compounds formed when hydrogen atoms occupy the interstitial spaces (the gaps) between metal atoms in a metallic lattice. These hydrides are typically formed with transition metals and some lanthanides and actinides. They can be represented by the general formula MHx, where M is the metal and x indicates the number of hydrogen atoms.

**Step 2: Characteristics of Interstitial Hydrides**
These hydrides are characterized by:
- They are usually non-stoichiometric, meaning that the ratio of hydrogen to metal can vary.
- They have metallic properties, such as electrical conductivity and malleability.
- They can absorb hydrogen gas and release it under certain conditions.

**Step 3: Define Molecular Hydrides**
Molecular hydrides, on the other hand, are compounds formed when hydrogen combines with non-metals or metalloids. They are typically represented by the formula XHn, where X is a non-metal and n is the number of hydrogen atoms. Examples include water (H2O), ammonia (NH3), and methane (CH4).

**Step 4: Characteristics of Molecular Hydrides**
Molecular hydrides are characterized by:
- They usually have definite stoichiometry, meaning the ratio of hydrogen to the other element is fixed.
- They tend to have covalent bonds and exhibit properties typical of molecular compounds, such as lower melting and boiling points compared to metallic hydrides.
- They are often gases or liquids at room temperature.

**Step 5: Differences Between Metallic and Molecular Hydrides**
The key differences between metallic (interstitial) hydrides and molecular hydrides include:
- **Composition**: Metallic hydrides involve metals and hydrogen, while molecular hydrides involve non-metals or metalloids and hydrogen.
- **Bonding**: Metallic hydrides exhibit metallic bonding, whereas molecular hydrides exhibit covalent bonding.
- **Properties**: Metallic hydrides have metallic properties (conductivity, malleability), while molecular hydrides have properties typical of covalent compounds (lower melting and boiling points).
- **Stoichiometry**: Metallic hydrides can be non-stoichiometric, while molecular hydrides have a definite stoichiometric ratio.

**Step 6: Conclusion**
In summary, metallic or interstitial hydrides are formed from metals and have metallic properties, while molecular hydrides are formed from non-metals and exhibit covalent characteristics. Understanding these differences helps in the study of hydrogen compounds and their applications in various fields.

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