Non-Metals and Their Compounds

Non-metals are elements that typically gain electrons to form negative ions (anions). In the JAMB syllabus, we focus on Hydrogen, Halogens, Oxygen, Sulphur, Nitrogen, and Carbon.

1. Hydrogen

Hydrogen is the simplest element.

• Commercial Production: Produced from Water Gas (a mixture of CO and H₂) by reacting steam with red-hot coke (C + H₂O → CO + H₂) or by cracking of petroleum fractions.
• Laboratory Preparation: Action of dilute HCl on zinc granules (Zn + 2HCl → ZnCl₂ + H₂).
• Test: A lighted splint applied to a test tube of hydrogen gives a 'pop' sound.
• Uses: Manufacture of ammonia (Haber process), hydrogenation of vegetable oils (margarine), and as rocket fuel.

2. Halogens (Focus on Chlorine)

Halogens are Group 7 elements. Chlorine is a greenish-yellow gas.

• Preparation: In the lab, by heating MnO₂ with concentrated HCl. Industrially, by the electrolysis of brine (NaCl solution) in the Nelson cell.
• Properties: A strong oxidizing agent and bleaching agent (only in the presence of water/moisture).
• Hydrogen Chloride (HCl): Prepared by the action of concentrated H₂SO₄ on rock salt (NaCl). It forms Hydrochloric acid when dissolved in water.
• Test for Chlorides: Add silver nitrate (AgNO₃) solution; a white precipitate (AgCl) forms, which is soluble in excess ammonia.

3. Oxygen and Sulphur

Oxygen:

• Production: Fractional distillation of liquid air.
• Oxides: Classified into Acidic (e.g., SO₂, CO₂), Basic (e.g., Na₂O, CaO), Amphoteric (e.g., Al₂O₃, ZnO), and Neutral (e.g., CO, N₂O, NO).
• Ozone (O₃): An allotrope of oxygen that protects the Earth from harmful UV radiation.

• Allotropes: Rhombic (stable at room temp) and Monoclinic (stable above 96°C).
• Sulphur(IV) Oxide (SO₂): Prepared by reacting Na₂SO₃ with dilute HCl. It acts as a reducing agent and a bleaching agent for wool/silk.
• Tetraoxosulphate(VI) Acid (H₂SO₄): Manufactured by the Contact Process using Vanadium(V) oxide (V₂O₅) as a catalyst. It is a strong acid, dehydrating agent, and oxidizing agent.

4. Nitrogen

• Ammonia (NH₃): Prepared in the lab by heating an ammonium salt with a strong base (e.g., Ca(OH)₂). Industrially via the Haber Process (Fe catalyst, 450°C, 200 atm).
• Trioxonitrate(V) Acid (HNO₃): Prepared from ammonia via the Ostwald process. It is a powerful oxidizing agent.
• Nitrogen Cycle: The process by which nitrogen is converted between its various chemical forms (fixation, nitrification, denitrification).

5. Carbon

• Allotropes: Diamond (hardest, non-conductor) and Graphite (soft, conductor).
• Carbon(IV) Oxide (CO₂): Prepared by dilute acid on carbonates. Used in fire extinguishers and photosynthesis.
• Carbon(II) Oxide (CO): Formed by incomplete combustion. It is toxic because it binds to hemoglobin more strongly than oxygen.
• Coal and Coke: Destructive distillation of coal yields coke, coal gas, ammoniacal liquor, and coal tar.