Tin (Sn) - Properties, Reactions & Uses

Tin (Sn) is a p-block element with significant historical and industrial relevance. Its characteristic properties, particularly its amphoteric nature and ability to exist in multiple oxidation states, make it an important topic for high school chemistry examinations. Applications range from protective coatings to essential alloy components.

CBSE/JEE Quick Revision Notes

• Symbol: Sn (from Latin stannum)
• Atomic Number (Z): 50
• Atomic Mass: 118.71 u
• Group: 14 (Carbon Family)
• Period: 5
• Block: p-block
• Valencies/Common Oxidation States: +2, +4 (most stable is +4 for lighter elements in Group 14, but +2 becomes more prominent for Sn and Pb due to inert pair effect).
• Nature: Soft, silvery-white metal. Exhibits allotropy (white tin, grey tin, rhombic tin).

Electron Configuration & Bonding Behavior

• Electronic Configuration: [Kr] 4d¹⁰ 5s² 5p²
• General Configuration (Group 14): ns² np²
• Oxidation States Explained:
  • +4 State: Achieved by the loss of all four valence electrons (two 5s and two 5p electrons). This state is more stable in many tin compounds, particularly with highly electronegative elements.
  • +2 State: Achieved by the loss of only the two 5p electrons. The reluctance of the 5s² electron pair to participate in bonding is known as the inert pair effect, which becomes prominent for heavier p-block elements like tin and lead. This makes the +2 oxidation state significant for tin.
• Bonding: Tin forms predominantly covalent compounds in its +4 oxidation state (e.g., SnCl₄). In its elemental form, it is a metal with metallic bonding.

Crucial Chemical Reactions

1. Reaction with Air/Oxygen

Tin burns in air or oxygen when heated to form tin(IV) oxide. Sn(s) + O₂(g) → SnO₂(s)

2. Reaction with Acids

• With Dilute Non-oxidizing Acids (e.g., HCl): Tin reacts to form tin(II) chloride and hydrogen gas. Sn(s) + 2HCl(aq) → SnCl₂(aq) + H₂(g)
• With Concentrated Nitric Acid: Tin is oxidized to form hydrated tin(IV) oxide (metastannic acid). Sn(s) + 4HNO₃(conc) → H₂SnO₃(s) + 4NO₂(g) + H₂O(l)
• With Dilute Nitric Acid: Forms tin(II) nitrate and nitric oxide. 3Sn(s) + 8HNO₃(dilute) → 3Sn(NO₃)₂(aq) + 2NO(g) + 4H₂O(l)
• With Concentrated Sulfuric Acid: Tin reacts to form tin(II) sulfate, sulfur dioxide, and water. Sn(s) + 2H₂SO₄(conc) → SnSO₄(aq) + SO₂(g) + 2H₂O(l)

3. Reaction with Halogens

Tin reacts readily with halogens to form tin halides, typically in the +4 oxidation state. Sn(s) + 2Cl₂(g) → SnCl₄(l)

4. Reaction with Alkalis (Amphoteric Nature)

Tin is an amphoteric metal, reacting with strong bases to form stannates.

• In +2 Oxidation State: Sn(s) + 2NaOH(aq) + 2H₂O(l) → Na₂[Sn(OH)₄](aq) + H₂(g) (Sodium tetrahydroxostannate(II)) (Alternatively, in older texts: Sn + 2NaOH → Na₂SnO₂ + H₂ forming sodium stannite)
• In +4 Oxidation State (Tin(IV) oxide): SnO₂(s) + 2NaOH(aq) → Na₂SnO₃(aq) + H₂O(l) (Sodium stannate(IV))

5. Important Compounds & Their Properties

• Tin(II) Chloride (SnCl₂):
  • Known as stannous chloride.
  • Powerful reducing agent due to the ease of oxidation from +2 to +4 state.
  • Example: 2FeCl₃(aq) + SnCl₂(aq) → 2FeCl₂(aq) + SnCl₄(aq)
  • Used in organic synthesis and as a mordant in dyeing.
• Tin(IV) Oxide (SnO₂):
  • Also known as stannic oxide or cassiterite (mineral form).
  • Amphoteric oxide.
  • Used in ceramics, glazes, and as a polishing agent.

Industrial and Biological Importance

1. Industrial Importance

• Tin Plating: Steel sheets are coated with a thin layer of tin to prevent corrosion, widely used in “tin cans” for food and beverage packaging.
• Alloys:
  • Bronze: (Copper + Tin) - historically significant, used in statues, coins, and engineering.
  • Pewter: (Tin + Copper, Antimony, Bismuth) - used for decorative items and tableware.
  • Solder: (Tin + Lead or Tin + Silver/Copper) - low melting point alloys for joining metals in electronics and plumbing.
• Float Glass Production: Molten glass is floated on a bed of molten tin to produce flat, smooth glass sheets.
• Catalysts: Certain tin compounds act as catalysts in various chemical processes.
• Organotin Compounds: Historically used as fungicides, pesticides, and PVC stabilizers. However, many uses are now restricted due to environmental concerns and toxicity.

2. Biological Importance

• Tin is a trace element, but its essentiality for humans is not clearly established.
• Organotin compounds can be highly toxic, especially to marine life and humans, due to their ability to interfere with cellular processes.