Group 15 Elements — Revision Notes

⚡ 30-Second Revision

Elements — N, P, As, Sb, Bi ($ns^2np^3$ configuration). \n- Trends: Atomic size $\uparrow$, Ionization Enthalpy $\downarrow$, Electronegativity $\downarrow$, Metallic Character $\uparrow$ (N, P non-metals; As, Sb metalloids; Bi metal). \n- Oxidation States: -3, +3, +5. Stability of +3 $\uparrow$ down group (inert pair effect); Stability of +5 $\downarrow$ down group. \n- Nitrogen Anomalies: Small size, high EN, no d-orbitals, $p\pi-p\pi$ bonding ($N\equiv N$), max covalency 4. \n- **Hydrides ($EH_3$)**: \n * Thermal stability: $NH_3 > PH_3 > AsH_3 > SbH_3 > BiH_3$ \n * Basicity: $NH_3 > PH_3 > AsH_3 > SbH_3 > BiH_3$ \n * Reducing character: $NH_3 < PH_3 < AsH_3 < SbH_3 < BiH_3$ \n- Oxides: $E_2O_3, E_2O_5$. Acidic $\rightarrow$ Amphoteric $\rightarrow$ Basic down group. \n- Halides: $EX_3, EX_5$. Nitrogen forms only $NX_3$. Stability of $EX_5$ $\downarrow$ down group. \n- Phosphorus Allotropes: White ($P_4$, reactive, poisonous, glows), Red (polymeric, less reactive), Black (most stable).

2-Minute Revision

Group 15 elements, or pnictogens, are characterized by their $ns^2np^3$ valence configuration. Key periodic trends include increasing atomic size and metallic character, and decreasing ionization enthalpy and electronegativity down the group.

Nitrogen exhibits unique anomalous behavior due to its small size, high electronegativity, and crucially, the absence of d-orbitals, which limits its covalency to four and enables stable $p\pi-p\pi$ multiple bonding (e.

g., in $N_2$). \n\nOxidation states range from -3 to +5. The stability of the +3 oxidation state increases down the group due to the inert pair effect, while the +5 state becomes less stable. Hydrides ($EH_3$) show decreasing thermal stability and basicity, but increasing reducing character, from $NH_3$ to $BiH_3$.

Oxides transition from acidic ($N_2O_3, P_4O_{10}$) to amphoteric ($As_2O_3, Sb_2O_3$) to basic ($Bi_2O_3$) down the group. Phosphorus exists in various allotropic forms (white, red, black), with white phosphorus being highly reactive and poisonous.

Remember the structures and properties of phosphorus oxoacids, especially the number of P-H and P-OH bonds determining their reducing nature and basicity.

5-Minute Revision

Group 15 elements (N, P, As, Sb, Bi) are pnictogens with $ns^2np^3$ configuration. As you move down the group, atomic size increases, ionization enthalpy and electronegativity decrease, and metallic character increases (N, P are non-metals; As, Sb are metalloids; Bi is a metal).

\n\nAnomalous Behavior of Nitrogen: Nitrogen is unique due to its small size, high electronegativity, and lack of d-orbitals. This allows it to form stable $p\pi-p\pi$ multiple bonds (e.g., $N\equiv N$ in $N_2$), making $N_2$ a gas.

It cannot expand its octet, limiting its maximum covalency to 4 (e.g., $NH_4^+$), unlike phosphorus which forms $PCl_5$ using d-orbitals. Nitrogen also forms strong hydrogen bonds in $NH_3$. \n\nOxidation States: Common states are -3, +3, +5.

The stability of the +3 state increases down the group (e.g., $Bi^{3+}$ is more stable than $Bi^{5+}$) due to the inert pair effect, where the $ns^2$ electrons are reluctant to bond. Conversely, the stability of the +5 state decreases down the group.

\n\n**Hydrides ($EH_3$)**: \n* Thermal Stability: Decreases ($NH_3 > PH_3 > AsH_3 > SbH_3 > BiH_3$) due to decreasing E-H bond strength. \n* Basicity: Decreases ($NH_3 > PH_3 > AsH_3 > SbH_3 > BiH_3$) due to decreasing electron density on the central atom.

\n* Reducing Character: Increases ($NH_3 < PH_3 < AsH_3 < SbH_3 < BiH_3$) due to weaker E-H bonds. \n\nOxides: Form $E_2O_3$ and $E_2O_5$. Acidic character decreases down the group. $N_2O_3, P_4O_{10}$ are acidic.

$As_2O_3, Sb_2O_3$ are amphoteric. $Bi_2O_3$ is basic. \n\nHalides: Form $EX_3$ and $EX_5$. Nitrogen only forms $NX_3$. $PCl_5$ is stable, but $BiCl_5$ is not, reflecting the decreasing stability of the +5 state.

\n\nAllotropy of Phosphorus: \n* **White Phosphorus ($P_4$)**: Tetrahedral, highly reactive (due to $60^\circ$ strain), poisonous, glows in dark, stored under water. \n* Red Phosphorus: Polymeric, less reactive, non-poisonous.

\n* Black Phosphorus: Most stable, layered structure. \n\nPhosphorus Oxoacids: \n* $H_3PO_2$ (Hypophosphorous acid): Monobasic, 2 P-H bonds, strong reducing agent. \n* $H_3PO_3$ (Phosphorous acid): Dibasic, 1 P-H bond, reducing agent.

\n* $H_3PO_4$ (Orthophosphoric acid): Tribasic, no P-H bonds, non-reducing. \nRemember, P-H bonds confer reducing properties, and P-OH bonds determine basicity.

Prelims Revision Notes

1
General Electronic Configuration — $ns^2np^3$. \n2. Atomic & Ionic Radii: Increase down the group. \n3. Ionization Enthalpy: Decreases down the group. Higher than Group 14 due to half-filled p-orbitals. \n4. Electronegativity: Decreases down the group. N is most electronegative. \n5. Metallic Character: Increases down the group (N, P non-metals; As, Sb metalloids; Bi metal). \n6. Oxidation States: \n * Common: -3, +3, +5. \n * Stability of +3 state $\uparrow$ down the group (inert pair effect). \n * Stability of +5 state $\downarrow$ down the group. \n7. Anomalous Behavior of Nitrogen: \n * Small size, high electronegativity, absence of d-orbitals. \n * Forms stable $p\pi-p\pi$ multiple bonds ($N\equiv N$). \n * Max covalency = 4 (cannot form $NX_5$). \n * Forms H-bonds (e.g., $NH_3$). \n8. **Hydrides ($EH_3$)**: \n * Thermal Stability: $NH_3 > PH_3 > AsH_3 > SbH_3 > BiH_3$. \n * Basicity: $NH_3 > PH_3 > AsH_3 > SbH_3 > BiH_3$. \n * Reducing Character: $NH_3 < PH_3 < AsH_3 < SbH_3 < BiH_3$. \n9. Oxides: \n * Form $E_2O_3$ and $E_2O_5$. \n * Acidic character: $N_2O_3, P_4O_{10}$ (acidic) $\rightarrow As_2O_3, Sb_2O_3$ (amphoteric) $\rightarrow Bi_2O_3$ (basic). \n10. Halides: \n * Form $EX_3$ and $EX_5$. \n * Nitrogen forms only $NX_3$. \n * Stability of $EX_5$ decreases down the group (e.g., $PCl_5$ stable, $BiF_5$ stable but $BiCl_5$ unstable). \n11. Allotropes of Phosphorus: \n * **White P ($P_4$)**: Tetrahedral, highly reactive, poisonous, chemiluminescent, stored under water. \n * Red P: Polymeric, less reactive, non-poisonous. \n * Black P: Most stable. \n12. Phosphorus Oxoacids: \n * $H_3PO_2$ (Hypophosphorous acid): +1 O.S., monobasic, 2 P-H bonds (strong reducing). \n * $H_3PO_3$ (Phosphorous acid): +3 O.S., dibasic, 1 P-H bond (reducing). \n * $H_3PO_4$ (Orthophosphoric acid): +5 O.S., tribasic, no P-H bonds (non-reducing). \n * Basicity = number of P-OH bonds. Reducing nature = presence of P-H bonds.

Vyyuha Quick Recall

N-P-As-Sb-Bi: New People Always Start Blogging. (For elements of Group 15)