Q.Describe the structure and reactivity of nitrogen trichloride, $\text{NCl}_3$, and state how it is prepared.

[!TLDR] NCl3 is prepared by chlorinating ammonia kept in large excess; it is pyramidal (sp3 N, like NH3) but highly unstable/explosive and readily hydrolysed to NH3 and HOCl. [!ANSWER] NCl3 is trigonal pyramidal (sp3 N), prepared from Cl2 + excess NH3, and is an unstable, explosive liquid that hydrolyses to ammonia and hypochlorous acid.

Nitrogen trichloride, $\text{NCl}_3$, is prepared by passing chlorine gas over ammonia kept in large excess (careful stoichiometric control is needed, since with insufficient excess ammonia the product can react further/decompose violently). Structurally it closely resembles ammonia: nitrogen is $sp^3$ hybridised, forming three $\sigma$ bonds to the three chlorine atoms with the fourth hybrid orbital holding the lone pair, giving a trigonal pyramidal shape with a Cl-N-Cl angle of about $107^\circ$. Despite this structural similarity to the stable ammonia molecule, $\text{NCl}_3$ is a pale-yellow, oily, and dangerously explosive liquid, since the N-Cl bonds are comparatively weak (nitrogen cannot use d orbitals to stabilise the arrangement the way phosphorus can), and it decomposes readily, sometimes on mere shock or slight heating, releasing nitrogen and chlorine. It is also readily hydrolysed by water: $\text{NCl}_3 + 3\text{H}_2\text{O} \rightarrow \text{NH}_3 + 3\text{HOCl}$ [!ANSWER] NCl3 is prepared from chlorine and excess ammonia, is trigonal pyramidal (sp3 nitrogen, like NH3), but is highly unstable/explosive and hydrolyses in water to ammonia and hypochlorous acid.

State the preparation (Cl2 + excess NH3), the structure by analogy with NH3 (sp3, pyramidal), and then the reactivity (explosive instability, hydrolysis products).

Assuming NCl3 is as stable as NH3 because the shapes are analogous; getting the hydrolysis products backwards (it gives NH3 + HOCl, not NCl3 back with acid).