General Reactions of Group 15 Elements

Group 15 elements, also known as the pnictogens, include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). These elements have diverse chemical properties but share some common reaction patterns due to their position in the periodic table. Understanding their general reactions is crucial for chemistry students, especially when preparing for exams.

Oxidation States and Trends

Group 15 elements exhibit a range of oxidation states, from -3 to +5. The stability of these oxidation states varies across the group.

Element	Common Oxidation States	Most Stable Oxidation State in Compounds
N	-3, +1, +2, +3, +4, +5	-3 in nitrides, +5 in nitrates
P	-3, +1, +3, +5	-3 in phosphides, +5 in phosphates
As	-3, +3, +5	-3 in arsenides, +3 in arsenites
Sb	-3, +3, +5	-3 in antimonides, +3 in antimonites
Bi	-3, +3, +5	+3 in bismuth compounds

General Reactions

Reaction with Oxygen

Group 15 elements react with oxygen to form oxides. The general formula for these oxides is E2O3 or E2O5, where E represents the element.

Examples:

• Nitrogen reacts with oxygen to form nitrogen dioxide (NO2) or dinitrogen pentoxide (N2O5):

[ 4NO_2 + O_2 \rightarrow 2N_2O_5 ]

• Phosphorus reacts with oxygen to form diphosphorus pentoxide (P2O5):

[ 4P + 5O_2 \rightarrow 2P_2O_5 ]

Reaction with Hydrogen

Group 15 elements form hydrides with the general formula EH3, where E is the element.

Examples:

• Nitrogen reacts with hydrogen to form ammonia (NH3):

[ N_2 + 3H_2 \rightarrow 2NH_3 ]

• Phosphorus reacts with hydrogen to form phosphine (PH3):

[ 2P + 3H_2 \rightarrow 2PH_3 ]

Reaction with Halogens

Group 15 elements react with halogens to form trihalides or pentahalides.

Examples:

• Nitrogen reacts with chlorine to form nitrogen trichloride (NCl3):

[ N_2 + 3Cl_2 \rightarrow 2NCl_3 ]

• Phosphorus reacts with fluorine to form phosphorus pentafluoride (PF5):

[ P + 5F_2 \rightarrow PF_5 ]

Reaction with Metals

Group 15 elements react with metals to form binary compounds known as pnictides with the general formula M3E, where M is the metal and E is the group 15 element.

Examples:

• Nitrogen reacts with lithium to form lithium nitride (Li3N):

[ 6Li + N_2 \rightarrow 2Li_3N ]

• Phosphorus reacts with sodium to form sodium phosphide (Na3P):

[ 3Na + P \rightarrow Na_3P ]

Acid-Base Behavior

Group 15 hydrides exhibit acid-base behavior. Ammonia (NH3) is a well-known base, while the heavier pnictogen hydrides tend to be more acidic.

Examples:

• Ammonia reacts with water to form ammonium ions (NH4+) and hydroxide ions (OH-):

[ NH_3 + H_2O \rightarrow NH_4^+ + OH^- ]

• Phosphine (PH3) can act as a Lewis base by donating its lone pair of electrons.

Hydrolysis Reactions

Group 15 halides are susceptible to hydrolysis, especially the higher halides.

Examples:

• Phosphorus trichloride (PCl3) reacts with water to form phosphorous acid (H3PO3) and hydrochloric acid (HCl):

[ PCl_3 + 3H_2O \rightarrow H_3PO_3 + 3HCl ]

• Phosphorus pentachloride (PCl5) hydrolyzes to phosphoric acid (H3PO4) and hydrochloric acid:

[ PCl_5 + 4H_2O \rightarrow H_3PO_4 + 5HCl ]

Conclusion

Group 15 elements show a variety of general reactions, including reactions with oxygen, hydrogen, halogens, and metals, as well as acid-base and hydrolysis reactions. These reactions are influenced by the element's oxidation state and its position in the periodic table. Understanding these reactions is essential for students to grasp the chemistry of Group 15 elements and to perform well in exams.