Hydride of Be is Covalent while that of Na is ionic Why ?

Answer

To understand why the hydride of beryllium (BeH₂) is covalent while that of sodium (NaH) is ionic, we need to consider the concepts of electronegativity and electropositivity.

### Step-by-Step Solution:

1. **Electronegativity and Electropositivity**:
- Electronegativity is the tendency of an atom to attract electrons towards itself in a chemical bond.
- Electropositivity is the tendency of an atom to lose electrons and form positive ions.

2. **Comparison of Beryllium and Sodium**:
- Beryllium (Be) is located in Group 2 of the periodic table and is less electropositive compared to sodium (Na), which is in Group 1.
- Sodium is more electropositive than beryllium, meaning sodium has a greater tendency to lose its outer electron.

3. **Formation of Hydrides**:
- When beryllium reacts with hydrogen, it forms beryllium hydride (BeH₂). Due to beryllium's higher electronegativity compared to sodium, it tends to share electrons with hydrogen rather than completely transferring them. This results in a covalent bond.
- In contrast, when sodium reacts with hydrogen, it forms sodium hydride (NaH). Sodium’s high electropositivity allows it to easily lose its outer electron to hydrogen, resulting in the formation of Na⁺ and H⁻ ions, which leads to an ionic bond.

4. **Conclusion**:
- Therefore, the hydride of beryllium is covalent because of its higher electronegativity and lower electropositivity, while the hydride of sodium is ionic due to its higher electropositivity and lower electronegativity.

### Summary:
- Beryllium (Be) forms covalent hydride (BeH₂) because it is less electropositive and more electronegative than sodium (Na), which forms ionic hydride (NaH) due to its higher electropositivity.