Reactions and uses

Reactions and Uses of Elements in Groups 15 to 18

The elements in Groups 15 to 18 of the periodic table, namely the pnictogens (Group 15), chalcogens (Group 16), halogens (Group 17), and noble gases (Group 18), exhibit a wide array of chemical reactions and have significant industrial, medical, and technological uses. These elements and their compounds play crucial roles in a variety of processes, from biological functions to industrial applications. This detailed exploration will cover the reactions of these elements and their numerous uses.

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Group 15: Pnictogens (Nitrogen Group)

Reactions of Group 15 Elements:

1. Nitrogen (N):
   • Reaction with Oxygen: Nitrogen reacts with oxygen at high temperatures to form nitrogen oxides (NOx), such as nitrogen monoxide (NO) and nitrogen dioxide (NO₂). This is the basis for the formation of smog and acid rain. N2+O2→2NON_2 + O_2 \rightarrow 2NON2​+O2​→2NO 2NO+O2→2NO22NO + O_2 \rightarrow 2NO_22NO+O2​→2NO2​
   • Reaction with Hydrogen: Nitrogen reacts with hydrogen in the Haber process to produce ammonia (NH₃), which is a key reaction in the production of fertilizers. N2+3H2→2NH3N_2 + 3H_2 \rightarrow 2NH_3N2​+3H2​→2NH3​
   • Formation of Nitric Acid: Nitrogen oxides react with water and oxygen to form nitric acid (HNO₃), an important industrial chemical. 2NO2+H2O+O2→2HNO32NO_2 + H_2O + O_2 \rightarrow 2HNO_32NO2​+H2​O+O2​→2HNO3​
2. Phosphorus (P):
   • Reaction with Oxygen: Phosphorus reacts with oxygen to form phosphorus oxides, such as diphosphorus pentoxide (P₄O₁₀). P4+5O2→P4O10P_4 + 5O_2 \rightarrow P_4O_{10}P4​+5O2​→P4​O10​
   • Reaction with Chlorine: Phosphorus reacts with chlorine to form phosphorus trichloride (PCl₃) and phosphorus pentachloride (PCl₅). P4+6Cl2→4PCl3P_4 + 6Cl_2 \rightarrow 4PCl_3P4​+6Cl2​→4PCl3​ P4+10Cl2→4PCl5P_4 + 10Cl_2 \rightarrow 4PCl_5P4​+10Cl2​→4PCl5​
3. Arsenic (As):
   • Reaction with Oxygen: Arsenic burns in air to form arsenic trioxide (As₂O₃). 4As+3O2→2As2O34As + 3O_2 \rightarrow 2As_2O_34As+3O2​→2As2​O3​
   • Reaction with Hydrogen: Arsenic reacts with hydrogen to form arsine (AsH₃), a highly toxic and flammable gas. 2As+3H2→2AsH32As + 3H_2 \rightarrow 2AsH_32As+3H2​→2AsH3​
4. Antimony (Sb):
   • Reaction with Oxygen: Antimony reacts with oxygen to form antimony trioxide (Sb₂O₃). 4Sb+3O2→2Sb2O34Sb + 3O_2 \rightarrow 2Sb_2O_34Sb+3O2​→2Sb2​O3​
   • Reaction with Chlorine: Antimony reacts with chlorine to form antimony trichloride (SbCl₃). Sb+Cl2→SbCl3Sb + Cl_2 \rightarrow SbCl_3Sb+Cl2​→SbCl3​
5. Bismuth (Bi):
   • Reaction with Oxygen: Bismuth reacts with oxygen to form bismuth oxide (Bi₂O₃). 4Bi+3O2→2Bi2O34Bi + 3O_2 \rightarrow 2Bi_2O_34Bi+3O2​→2Bi2​O3​
   • Reaction with Chlorine: Bismuth reacts with chlorine to form bismuth trichloride (BiCl₃). Bi+Cl2→BiCl3Bi + Cl_2 \rightarrow BiCl_3Bi+Cl2​→BiCl3​

Uses of Group 15 Elements:

1. Nitrogen:
   • Ammonia Production: Nitrogen is used in the Haber process to produce ammonia (NH₃), which is a critical raw material for fertilizers.
   • Cryogenics: Liquid nitrogen is used as a coolant in cryogenics due to its extremely low boiling point (-196°C).
   • Inert Atmosphere: Nitrogen gas is used to provide an inert atmosphere in chemical processes, preventing oxidation.
2. Phosphorus:
   • Fertilizers: Phosphorus compounds, particularly phosphates, are used extensively in fertilizers to promote plant growth.
   • Detergents: Phosphates are used in detergents to soften water and enhance cleaning efficiency.
   • Flame Retardants: Phosphorus compounds are used as flame retardants in plastics and textiles.
3. Arsenic:
   • Semiconductors: Arsenic is used in the production of semiconductors, such as gallium arsenide (GaAs), which is used in high-speed electronic devices and solar cells.
   • Wood Preservatives: Arsenic compounds, such as chromated copper arsenate (CCA), are used as preservatives for wood.
   • Poison: Arsenic compounds have historically been used as poisons, though their use has been restricted due to toxicity.
4. Antimony:
   • Flame Retardants: Antimony compounds are used as flame retardants in plastics and textiles.
   • Alloys: Antimony is used in alloys to increase their hardness and durability, particularly in lead-based alloys for batteries.
5. Bismuth:
   • Pharmaceuticals: Bismuth compounds, such as bismuth subsalicylate, are used to treat gastrointestinal disorders like diarrhea and indigestion.
   • Low-melting Alloys: Bismuth is used in low-melting point alloys for applications like fire safety devices and solders.

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Group 16: Chalcogens (Oxygen Group)

Reactions of Group 16 Elements:

1. Oxygen (O):
   • Reaction with Hydrogen: Oxygen reacts with hydrogen to form water (H₂O), an exothermic reaction that releases a significant amount of energy. 2H2+O2→2H2O2H_2 + O_2 \rightarrow 2H_2O2H2​+O2​→2H2​O
   • Reaction with Metals: Oxygen reacts with metals to form metal oxides, such as iron(III) oxide (Fe₂O₃) from iron. 3Fe+4O2→2Fe2O33Fe + 4O_2 \rightarrow 2Fe_2O_33Fe+4O2​→2Fe2​O3​
2. Sulfur (S):
   • Reaction with Oxygen: Sulfur reacts with oxygen to form sulfur dioxide (SO₂), and further oxidation forms sulfur trioxide (SO₃). S+O2→SO2S + O_2 \rightarrow SO_2S+O2​→SO2​ 2SO2+O2→2SO32SO_2 + O_2 \rightarrow 2SO_32SO2​+O2​→2SO3​
   • Reaction with Metals: Sulfur reacts with metals, such as zinc or iron, to form metal sulfides like zinc sulfide (ZnS) and iron sulfide (FeS).
3. Selenium (Se):
   • Reaction with Oxygen: Selenium reacts with oxygen to form selenium dioxide (SeO₂). Se+O2→SeO2Se + O_2 \rightarrow SeO_2Se+O2​→SeO2​
   • Reaction with Hydrogen: Selenium reacts with hydrogen to form hydrogen selenide (H₂Se), a toxic gas. Se+H2→H2SeSe + H_2 \rightarrow H_2SeSe+H2​→H2​Se
4. Tellurium (Te):
   • Reaction with Oxygen: Tellurium reacts with oxygen to form tellurium dioxide (TeO₂). Te+O2→TeO2Te + O_2 \rightarrow TeO_2Te+O2​→TeO2​
5. Polonium (Po):
   • Radioactive Decay: Polonium undergoes alpha decay, emitting alpha particles and transforming into stable lead isotopes.
   • Reaction with Oxygen: Polonium reacts with oxygen to form polonium dioxide (PoO₂), though this is a rare reaction due to the radioactivity of polonium.

Uses of Group 16 Elements:

1. Oxygen:
   • Respiration: Oxygen is essential for respiration in animals and is vital for most life forms on Earth.
   • Medical Applications: Oxygen is used in medical therapies, especially for patients with respiratory conditions such as asthma, COPD, or in emergency situations like suffocation.
   • Steel Production: Oxygen is used in the production of steel by providing a pure source of oxygen for the oxidation of impurities in molten iron.
2. Sulfur:
   • Fertilizers: Sulfur is an essential element for plants, and sulfur compounds are used in fertilizers to improve crop yields.
   • Sulfuric Acid: Sulfuric acid is one of the most important industrial chemicals, used in the manufacture of fertilizers, cleaning agents, and in petroleum refining.
   • Vulcanization of Rubber: Sulfur is used in the vulcanization of rubber, a process that improves the elasticity and durability of rubber products.
3. Selenium:
   • Electronics: Selenium is used in photovoltaic cells (solar cells) and in the production of rectifiers and photocells.
   • Glass Manufacturing: Selenium is used in the production of colored glass, particularly to produce red and pink hues.
4. Tellurium:
   • Semiconductors: Tellurium is used in the production of semiconductors, especially in solar cells and thermoelectric devices.
   • Alloys: Tellurium is used in alloys to improve their machinability and wear resistance, such as in lead alloys for batteries.
5. Polonium:
   • Radiation Source: Polonium is used as a radiation source in devices like static eliminators and in some types of nuclear reactors.
   • Research: Due to its radioactivity, polonium is used in scientific research, particularly in the study of nuclear reactions.

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Group 17: Halogens (Halogen Group)

Reactions of Group 17 Elements:

1. Fluorine (F):
   • Reaction with Metals: Fluorine reacts with almost all metals to form metal fluorides.
   • Reaction with Hydrogen: Fluorine reacts violently with hydrogen to form hydrogen fluoride (HF). H2+F2→2HFH_2 + F_2 \rightarrow 2HFH2​+F2​→2HF
2. Chlorine (Cl):
   • Reaction with Water: Chlorine reacts with water to form hydrochloric acid (HCl) and hypochlorous acid (HOCl). Cl2+H2O→HCl+HOClCl_2 + H_2O \rightarrow HCl + HOClCl2​+H2​O→HCl+HOCl
3. Bromine (Br):
   • Reaction with Metals: Bromine reacts with metals to form metal bromides. 2Na+Br2→2NaBr2Na + Br_2 \rightarrow 2NaBr2Na+Br2​→2NaBr
4. Iodine (I):
   • Reaction with Hydrogen: Iodine reacts with hydrogen to form hydrogen iodide (HI). H2+I2→2HIH_2 + I_2 \rightarrow 2HIH2​+I2​→2HI

Uses of Halogens:

1. Fluorine:
   • Fluoride Compounds: Fluorine is used to produce fluoride compounds, which are used in water fluoridation, toothpaste, and the manufacture of Teflon.
   • Nuclear Industry: Fluorine compounds, particularly uranium hexafluoride (UF₆), are used in uranium enrichment for nuclear fuel production.
2. Chlorine:
   • Water Treatment: Chlorine is widely used in water treatment to disinfect drinking water and swimming pools.
   • Production of PVC: Chlorine is used in the manufacture of polyvinyl chloride (PVC), a plastic used in pipes, flooring, and various other products.
3. Bromine:
   • Flame Retardants: Bromine compounds are used as flame retardants in plastics and textiles.
   • Pesticides: Bromine is used in the production of certain pesticides, particularly in agricultural applications.
4. Iodine:
   • Antiseptics: Iodine is used as an antiseptic in the form of tinctures or iodophors.
   • Medical Imaging: Iodine is used in medical imaging, particularly in contrast agents for X-rays and CT scans.

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Group 18: Noble Gases

Reactions of Noble Gases:

Noble gases are generally chemically inert due to their full valence shells. However, under extreme conditions, certain noble gases can form compounds, particularly with highly electronegative elements like fluorine.

1. Xenon: Xenon can form compounds like xenon hexafluoride (XeF₆) with fluorine under high pressure.
2. Krypton: Krypton can form krypton difluoride (KrF₂) with fluorine.
3. Helium: Helium is inert and does not readily form compounds, but it can be used in the formation of superfluid helium-3 and helium-4 at very low temperatures.

Uses of Noble Gases:

1. Helium:
   • Cryogenics: Helium is used as a coolant in cryogenic applications due to its extremely low boiling point.
   • Lifting Gas: Helium is used in balloons and airships because it is lighter than air and nonflammable.
2. Neon:
   • Signs and Lighting: Neon is widely used in neon signs and lighting due to its ability to emit bright colors when electrified.
3. Argon:
   • Welding: Argon is used in welding as an inert gas to shield the welding area from oxidation.
4. Krypton and Xenon:
   • Specialized Lighting: Both krypton and xenon are used in specialized lighting, such as high-performance light bulbs and lamps.
5. Radon:
   • Radiotherapy: Radon is used in radiotherapy for cancer treatment, although its use is limited due to its radioactivity.

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10 Questions and Answers Regarding the Reactions

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1. What is the primary industrial use of nitrogen?

Answer: Nitrogen is primarily used in the production of ammonia through the Haber process. Ammonia is a key ingredient in fertilizers, which are essential for modern agriculture. Nitrogen is also used to create an inert atmosphere in industries like food packaging, chemical manufacturing, and electronics.

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2. How does sulfur react with oxygen, and what are the industrial uses of sulfur dioxide?

Answer: Sulfur reacts with oxygen to form sulfur dioxide (SO₂):S+O2→SO2S + O_2 \rightarrow SO_2S+O2​→SO2​

Sulfur dioxide is used in the production of sulfuric acid (H₂SO₄), one of the most important industrial chemicals, which is used in fertilizer production, petroleum refining, and chemical synthesis. Additionally, sulfur dioxide is used as a preservative in food and beverages.

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3. What is the significance of oxygen in combustion reactions?

Answer: Oxygen is essential for combustion reactions as it supports the oxidation of fuels, such as carbon, hydrogen, and hydrocarbons. When a fuel burns in the presence of oxygen, it produces energy in the form of heat and light, releasing carbon dioxide and water as by-products:C+O2→CO2C + O_2 \rightarrow CO_2C+O2​→CO2​

This process is fundamental for energy production in engines, heating, and industrial applications.

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4. Why is chlorine used in water treatment?

Answer: Chlorine is used in water treatment because of its powerful disinfecting properties. It kills harmful bacteria, viruses, and other pathogens, making water safe to drink. Chlorine is often added to drinking water, swimming pools, and sewage treatment facilities to ensure the water is free of contaminants and disease-causing organisms.

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5. What is the role of iodine in medical applications?

Answer: Iodine is commonly used in medicine, particularly in antiseptics and disinfectants. It is often used as a tincture or in iodine-based solutions to clean wounds and prevent infection. Iodine is also used as a contrast agent in medical imaging, especially in X-ray and CT scans, to enhance the visibility of certain body structures.

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6. How is fluorine used in industrial applications?

Answer: Fluorine is used extensively in various industrial applications, especially in the production of fluorocarbons like Teflon (PTFE), which is used for non-stick cookware, electrical insulation, and in the chemical industry. Fluorine is also crucial in the production of uranium hexafluoride (UF₆) for nuclear fuel processing and in the fluoridation of drinking water to prevent tooth decay.

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7. What are the uses of noble gases, particularly helium and neon?

Answer: Helium is used in cryogenics, for example, in cooling superconducting magnets, as well as in airships and balloons because it is lighter than air and non-flammable. Neon is used primarily in neon signs and specialized lighting because it emits a distinct red-orange glow when electrically excited. Both gases are also used in various scientific and technological applications due to their inert properties.

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8. What is the importance of phosphorus in agriculture?

Answer: Phosphorus is a vital nutrient for plants, playing a key role in photosynthesis, energy transfer, and cell division. It is primarily used in fertilizers, particularly as phosphate (PO₄³⁻) compounds, to enhance crop yields. Phosphorus-based fertilizers are essential for ensuring plant growth and food production worldwide.

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9. What is the environmental impact of nitrogen oxides (NOx)?

Answer: Nitrogen oxides (NOx), including nitrogen monoxide (NO) and nitrogen dioxide (NO₂), have significant environmental impacts. They are primary contributors to air pollution, particularly in the formation of smog and acid rain. NOx reacts with water vapor and oxygen in the atmosphere to form nitric acid (HNO₃), which can damage ecosystems, soil, and water bodies. They also contribute to respiratory problems in humans.

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10. How does the reactivity of halogens change down the group?

Answer: As you move down Group 17 (halogens), their reactivity decreases. Fluorine is the most reactive halogen due to its small size and high electronegativity, making it highly efficient at accepting electrons. Chlorine, bromine, and iodine become progressively less reactive as the atomic size increases and the electronegativity decreases. This trend affects their ability to form bonds and their effectiveness as oxidizing agents.

Index NCERT 12th Class Chemistry