Explain why the bond angle in ${\mathrm{N}\mathrm{H}}_3$ is larger than in ${\mathrm{P}\mathrm{H}}_3$?

<p>The reason why bond angle is larger in <math><msub><mrow><mrow><mi mathvariant="normal">N</mi><mi mathvariant="normal">H</mi></mrow></mrow><mrow><mrow><mn>3</mn></mrow></mrow></msub></math> than &nbsp;<span contenteditable="false"><math><msub><mrow><mrow><mi mathvariant="normal">P</mi><mi mathvariant="normal">H</mi></mrow></mrow><mrow><mrow><mn>3</mn></mrow></mrow></msub></math></span> are given below.</p><ul><li>In <math><msub><mrow><mrow><mi mathvariant="normal">N</mi><mi mathvariant="normal">H</mi></mrow></mrow><mrow><mrow><mn>3</mn></mrow></mrow></msub></math> , there is one lone pair on the nitrogen atom increases repulsion, while the lone pair on phosphorus is in a higher energy orbital and causes less repulsion.</li><li>Nitrogen is a small and electronegative atom whereas phosphorus is larger and less electronegative than nitrogen.</li><li>In &nbsp;<span contenteditable="false"><math><msub><mrow><mrow><mi mathvariant="normal">P</mi><mi mathvariant="normal">H</mi></mrow></mrow><mrow><mrow><mn>3</mn></mrow></mrow></msub></math></span>, the bonding orbitals are nearly pure p-orbitals, which are less directionals–p hybridization, on the other hand, the bond pairs remain fairly directed, leading to a larger bond angle.</li></ul><p>Hence, the bond angle in <math><msub><mrow><mrow><mi mathvariant="normal">N</mi><mi mathvariant="normal">H</mi></mrow></mrow><mrow><mrow><mn>3</mn></mrow></mrow></msub></math> is about 107° ( less than the ideal tetrahedral 109.5°) due to lone pair presence and highly electronegative atom, and the bond angle in PH? ( 93.5°) is much smaller due to less repulsive lone pair, and less electronegative atom.</p><p>Hence, the bond angle in&nbsp;<span contenteditable="false"><math><msub><mrow><mrow><mi mathvariant="normal">N</mi><mi mathvariant="normal">H</mi></mrow></mrow><mrow><mrow><mn>3</mn></mrow></mrow></msub></math>&nbsp;</span> (107°) is larger than in&nbsp;<span contenteditable="false"><math><msub><mrow><mrow><mi mathvariant="normal">P</mi><mi mathvariant="normal">H</mi></mrow></mrow><mrow><mrow><mn>3</mn></mrow></mrow></msub></math></span> (93.5°).</p><p>&nbsp;</p><p>&nbsp;</p>

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