Question

Why is PCl\(_5\) a known compound, but NCl\(_3\) is not?

Hint:

Phosphorus can expand its valence shell, allowing for stable compounds like PCl\(_5\), whereas nitrogen cannot, making NCl\(_3\) unstable.

Answer 1

Step 1: Analyze the structure and stability of PCl\(_5\) and NCl\(_3\).
- PCl\(_5\) (phosphorus pentachloride) is a stable compound because phosphorus can expand its valence shell to accommodate five chlorine atoms. Phosphorus has a relatively large atomic size and can form stable bonds with chlorine atoms. The molecule adopts a trigonal bipyramidal structure, which is stable. - NCl\(_3\) (nitrogen trichloride), however, is not as stable. Nitrogen is smaller and does not have the ability to expand its valence shell in the same way phosphorus does. Therefore, nitrogen can only form three bonds, making NCl\(_3\) less stable. Additionally, NCl\(_3\) is highly reactive and unstable, especially when exposed to heat or light, making it difficult to isolate.
Step 2: Conclusion.
- PCl\(_5\) is stable due to the ability of phosphorus to form five bonds, while NCl\(_3\) is unstable because nitrogen cannot accommodate more than three bonds.
Final Answer: PCl\(_5\) is stable because phosphorus can expand its valence shell to form five bonds, whereas NCl\(_3\) is unstable because nitrogen cannot expand its valence shell beyond three bonds.
Final Answer: \[ \boxed{\text{PCl}_5 \text{ is stable due to the ability of phosphorus to form five bonds, while NCl}_3 \text{ is unstable due to nitrogen's inability to form more than three bonds.}} \]