Silver (Ag): Properties, Reactions, and Uses

Introduction to Silver (Ag)

Silver (Ag) is a precious transition metal known for its distinct luster, high electrical and thermal conductivity, and chemical inertness under ambient conditions. Beyond its traditional use in jewelry and coinage, silver plays a vital role in modern technology, medicine, and industrial applications due to its unique physical and chemical properties. Its historical significance and diverse applications make it a crucial element for study in chemistry curricula.

CBSE/JEE Quick Revision Notes

• Atomic Number (Z): 47
• Atomic Mass (A): 107.868 g/mol
• Symbol: Ag (from Latin argentum)
• Group: 11 (formerly IB)
• Period: 5
• Block: d-block (Transition Metal)
• Appearance: Soft, white, lustrous metal; highest electrical and thermal conductivity of all metals.
• Density: 10.49 g/cm³
• Melting Point: 961.78 °C
• Boiling Point: 2162 °C
• Common Oxidation State: +1 (most stable). Less common +2 (e.g., AgF₂) and +3.
• Nature: Malleable and ductile. Does not react with oxygen or water at room temperature. Tarnishes upon exposure to sulfur compounds in the air.

Electron Configuration & Bonding Behavior

Electron Configuration

The ground state electron configuration of Silver is an exception to the Aufbau principle due to the stability associated with a completely filled d-subshell.

• Standard Configuration: [Kr] 4d¹⁰ 5s¹
  • This configuration provides exceptional stability due to the fully filled 4d subshell.

Bonding Behavior

Silver predominantly exhibits a +1 oxidation state by losing its single 5s electron.

• Ionic Bonding: Forms ionic compounds with highly electronegative non-metals, such as halides (e.g., AgCl, AgBr, AgI). Most silver(I) compounds are white in color.
• Covalent Character: While forming ionic bonds, silver compounds often display significant covalent character, particularly with larger anions.
• Complex Formation: Silver(I) has a strong tendency to form linear, two-coordinate complex ions, such as the diamminesilver(I) ion, [Ag(NH₃)₂]⁺ (a key component of Tollens’ reagent).
• Oxidation State +2: Less common, typically observed in strong oxidizing environments or with highly electronegative elements (e.g., AgF₂).

Crucial Chemical Reactions

1. Tarnishing of Silver

Silver tarnishes in the presence of hydrogen sulfide (H₂S) gas and oxygen, forming black silver sulfide (Ag₂S). 4Ag(s) + 2H₂S(g) + O₂(g) → 2Ag₂S(s) + 2H₂O(l)

2. Reaction with Halogens

Silver reacts readily with halogens, particularly chlorine and bromine, to form silver halides. These halides are notably photosensitive.

• 2Ag(s) + Cl₂(g) → 2AgCl(s) (White precipitate, turns violet on exposure to light)
• 2Ag(s) + Br₂(l) → 2AgBr(s) (Pale yellow precipitate, turns dark on exposure to light)
• 2Ag(s) + I₂(s) → 2AgI(s) (Yellow precipitate, less photosensitive than AgBr)
• 2Ag(s) + F₂(g) → 2AgF(s) (Silver fluoride is soluble in water, unlike other silver halides)

3. Reaction with Acids

• With Dilute Nitric Acid: Silver reacts with dilute nitric acid to produce silver nitrate, nitric oxide, and water. 3Ag(s) + 4HNO₃(dilute) → 3AgNO₃(aq) + NO(g) + 2H₂O(l)
• With Concentrated Nitric Acid: Reaction with concentrated nitric acid yields silver nitrate, nitrogen dioxide, and water. Ag(s) + 2HNO₃(conc) → AgNO₃(aq) + NO₂(g) + H₂O(l)
• With Non-oxidizing Acids: Silver does not react with non-oxidizing acids like HCl or H₂SO₄ because its standard electrode potential (+0.80 V) is higher than that of hydrogen.

4. Precipitation of Silver Halides (Qualitative Analysis)

Silver nitrate solution is used to detect halide ions (Cl⁻, Br⁻, I⁻).

• Chloride: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq) (White precipitate, soluble in excess aqueous ammonia)
• Bromide: AgNO₃(aq) + NaBr(aq) → AgBr(s) + NaNO₃(aq) (Pale yellow precipitate, sparingly soluble in excess aqueous ammonia)
• Iodide: AgNO₃(aq) + NaI(aq) → AgI(s) + NaNO₃(aq) (Yellow precipitate, insoluble in excess aqueous ammonia)

5. Formation of Silver Mirror (Tollens’ Test)

This reaction is a key test for aldehydes in organic chemistry. Aldehydes reduce diamminesilver(I) ion ([Ag(NH₃)₂]⁺, a component of Tollens’ reagent) to metallic silver, forming a “silver mirror” on the inner surface of the test tube. RCHO + 2[Ag(NH₃)₂]⁺(aq) + 3OH⁻(aq) → RCOO⁻(aq) + 2Ag(s) + 4NH₃(aq) + 2H₂O(l)

Industrial and Biological Importance

Industrial Importance

1. Photography: Silver halides (AgBr, AgCl) are crucial components of photographic films and papers due to their photosensitive nature, undergoing photochemical decomposition upon exposure to light.
2. Jewelry and Coinage: Its aesthetic appeal, luster, and resistance to corrosion (though it tarnishes) make it highly valued. It is often alloyed with copper (e.g., sterling silver, 92.5% Ag, 7.5% Cu) to increase its hardness and durability.
3. Electrical and Electronics: Highest electrical conductivity among all metals, used in electrical contacts, circuits, and high-performance conductors.
4. Mirrors: Excellent reflectivity makes it ideal for coating mirrors.
5. Batteries: Used in silver-oxide batteries (Ag₂O), which offer high energy density and stable voltage.
6. Catalysis: Employed as a catalyst in certain industrial oxidation reactions, such as the production of ethylene oxide.
7. Medical Imaging: Silver nanoparticles are being researched for use in various medical imaging techniques.

Biological Importance

1. Antimicrobial Agent: Silver ions (Ag⁺) possess potent antimicrobial and antiseptic properties. They interfere with bacterial cell respiration and metabolism.
   • Used in wound dressings, medical coatings (e.g., catheters), and water purification systems.
   • Colloidal silver solutions are used as disinfectants.
2. Toxicity: While antimicrobial, excessive exposure or ingestion of silver compounds can lead to argyria, a condition causing bluish-grey discoloration of the skin, eyes, and internal organs due to silver deposition. Silver is not considered an essential trace element for humans.