The Nitrogen Group corresponds to Group 15 (5A) of the Periodic Table and includes elements with five valence electrons (general configuration ns² np³). Because of this configuration, the pnictogens can exhibit a wide range of oxidation states, especially −3, +3, and +5. The maximum state +5 occurs when all valence electrons participate in bonding, though its stability decreases significantly for the heavier members due to the inert pair effect. Compounds of Group 15 elements generally reflect high ionization energies compared with metallic groups.
Members of the Nitrogen Group
- Nitrogen (N) – nonmetal, exists as a diatomic N₂ molecule with an exceptionally strong triple bond;
- Phosphorus (P) – nonmetal, shows allotropy (white, red, black phosphorus);
- Arsenic (As) – typical metalloid with several allotropes;
- Antimony (Sb) – metalloid with enhanced metallic character;
- Bismuth (Bi) – heavy metal, most stable in the +3 oxidation state;
- Moscovium (Mc) – synthetic superheavy element (formerly ununpentium – Uup), extremely unstable with no practical applications.
General properties and periodic trends
- Electronegativity and metallic character: electronegativity decreases from N to Bi, while metallic character increases. Thus, N and P are nonmetals; As and Sb are metalloids; Bi is metallic.
- Covalent radii: increase down the group, reducing the strength of X–X and X–H bonds.
- Oxidation states: N and P often display +5 and +3 (and −3 in hydrides and salts). As and Sb switch between +3 and +5, while Bi favors +3.
- Ionization energy: relatively high compared to metals; decreases gradually down the group.
Elemental structures and allotropy
- Nitrogen (N₂): the only stable diatomic molecule of the group, its strong N≡N triple bond gives low reactivity under normal conditions.
- Phosphorus: occurs as white, red, and black allotropes, each with different reactivity; white phosphorus is highly reactive and must be stored carefully.
- Arsenic, antimony, and bismuth: typically form layered or metallic structures, with conductivity increasing from As to Bi.
Hydrides and stability trends
The hydrides of Group 15 show clear periodic patterns:
- NH₃ (ammonia): stable, basic, strong N–H bonds, bond angle around 107°;
- PH₃ (phosphine), AsH₃ (arsine), SbH₃ (stibine), and BiH₃ (bismuthine): become progressively less stable down the group, with lower bond energies, smaller bond angles (~90–95°), and higher toxicity in the heavier hydrides.
Oxides, oxoacids, and acid–base behavior
- Nitrogen: forms a wide range of oxides (NO, NO₂, N₂O, N₂O₃, N₂O₄, N₂O₅) and acids such as nitric acid (HNO₃) and nitrous acid (HNO₂), many with significant oxidizing properties and environmental impact.
- Phosphorus: produces P₂O₃ and P₂O₅ (often written as P₄O₆ and P₄O₁₀), leading to phosphorous acid (H₃PO₃) and phosphoric acid (H₃PO₄). Phosphates are essential in biology and widely used in agriculture and industry.
- As, Sb, Bi: form oxides in +3 and +5 states; their amphoteric nature is evident, especially in Sb₂O₃ and Bi₂O₃, reflecting the rise in metallic character.
Reactivity and bonding
- Multiple bonding: common for nitrogen (N≡N, C≡N, N=O), less so for phosphorus, and rare in As, Sb, and Bi, which prefer single bonds with lone pairs.
- With metals: forms nitrides and phosphides important in advanced materials; arsenides, antimonides, and bismuthides are used in semiconductors and alloys.
Occurrence, processes, and applications
- Nitrogen: the main component of the Earth’s atmosphere; converted to ammonia in the Haber–Bosch process, the basis of global fertilizer production.
- Phosphorus: found in phosphate minerals (apatite); vital to life (DNA, ATP); used in fertilizers, flame retardants, alloys, and surface treatments.
- Arsenic: occurs in sulfide minerals; historically used in pesticides and still relevant in GaAs semiconductors; requires strict control due to toxicity.
- Antimony: used in alloys to increase hardness, in flame retardants, and in some electronics.
- Bismuth: less toxic than most heavy metals; used in medicines (bismuth subsalicylate), cosmetics, low-melting alloys, and lead-free solders.
- Moscovium: produced in trace amounts under laboratory conditions; highly unstable with limited chemical data.
Environmental and safety aspects
- Ammonia and nitrogen oxides: essential in industry and agriculture but NOx emissions harm air quality, contribute to acid rain, and promote tropospheric ozone formation.
- Phosphates: essential for crops; excess causes eutrophication in water systems, making management critical.
- Arsine (AsH₃), stibine (SbH₃), and bismuthine (BiH₃): extremely toxic, requiring strict safety protocols in labs and industry.
FAQ – Frequently Asked Questions about the Nitrogen Family
Which elements belong to the Nitrogen Family?
Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), Bismuth (Bi), and Moscovium (Mc) (formerly Uup, synthetic and unstable).
Why is nitrogen the only diatomic element in the group?
Because the N≡N triple bond is exceptionally strong and stable. In P, As, Sb, and Bi, larger atoms and weaker bonding prevent stable X₂ molecules.
Is the +5 oxidation state always stable?
No. While possible for several pnictogens, the stability of +5 decreases from P to Bi. In Bi, the +3 state is dominant due to the inert pair effect.
How do hydride stability and basicity vary?
From NH₃ to BiH₃, X–H bonds weaken, bond angles shrink, basicity decreases, and toxicity increases in the heavier hydrides.
What are the main applications of Group 15 elements?
Ammonia and derivatives in fertilizers; phosphates in agriculture and industry; arsenides in semiconductors; and specialized alloys and materials from Sb and Bi.