Chemistry: Elements, Acids, Bases & Compounds
Chemistry: Elements, Acids, Bases और Compounds
Chemistry: Elements, Acids, Bases & Compounds
- General Science
- Chemistry: Elements, Acids, Bases & Compounds
Recall atomic structure, the periodic table, acids and bases with the pH scale, common metals and everyday compounds.
🎯 Learning Objective
Recall atomic structure, the periodic table, acids and bases with the pH scale, common metals and everyday compounds.
💡 Concept
- An atom has protons (positive) and neutrons (neutral) in the nucleus, with electrons (negative) orbiting it; the atomic number equals the number of protons
- Dmitri Mendeleev is the 'Father of the Periodic Table'; the modern periodic law arranges elements by atomic number
- Hydrogen (atomic number 1) is the lightest element; oxygen is the most abundant element in the Earth's crust and aluminium the most abundant metal
- Some Latin-based symbols: Sodium = Na, Potassium = K, Iron = Fe, Gold = Au, Silver = Ag, Copper = Cu, Lead = Pb
- Acids taste sour, turn blue litmus red and have pH below 7 — examples are hydrochloric acid (HCl, in the stomach), sulphuric acid (H2SO4, the 'king of chemicals') and citric acid (in lemons)
- Bases taste bitter, feel soapy, turn red litmus blue and have pH above 7 — examples are sodium hydroxide (NaOH) and calcium hydroxide (lime water)
- The pH scale runs 0 to 14; 7 is neutral (pure water), below 7 is acidic and above 7 is basic; acid + base gives salt + water (neutralisation)
- Mercury is the only metal that is liquid at room temperature; gold and silver are the least reactive (noble) metals
- Common alloys: Brass = copper + zinc, Bronze = copper + tin, Steel = iron + carbon, Stainless steel = iron + chromium + nickel
- Everyday compounds: Baking soda = sodium bicarbonate (NaHCO3), Washing soda = sodium carbonate (Na2CO3), Common salt = sodium chloride (NaCl), Marble = calcium carbonate (CaCO3)
🧮 Key Formulas
pH: 0-14 (7 neutral, below 7 acidic, above 7 basic)
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Baking soda NaHCO3 | Washing soda Na2CO3 | Common salt NaCl | Marble CaCO3
✏️ Easy Example
Q. Which is the only metal that is liquid at room temperature? (a) Sodium (b) Mercury (c) Bromine (d) Aluminium
- Bromine is a liquid but a non-metal
- Mercury is the only metal that stays liquid at room temperature
Answer: (b) Mercury
🇮🇳 Real-Life Example
The baking soda in your kitchen is sodium bicarbonate; drop it in acidic curd or lemon and it fizzes because an acid-base reaction releases carbon dioxide gas — the same fizz that makes cakes and dhoklas rise.
📝 Exam-Level Example
Q. Which gas is the most abundant in the Earth's atmosphere?
- Air is roughly 78% of one gas and 21% oxygen
- Nitrogen is the most abundant atmospheric gas
Answer: Nitrogen
📝 Exam-Level Example
Q. Brass is an alloy of which two metals?
- Brass is a common yellow alloy used in utensils
- It is made of copper and zinc
Answer: Copper and zinc
🪄 Memory Trick
Alloys: Brass = Copper + Zinc ('BraZZ' hints Zinc), Bronze = Copper + Tin. pH memory: 'below 7 = acid (lemon), above 7 = base (soap)'.
⚠️ Common Mistakes
- ❌ Confusing baking soda (NaHCO3) with washing soda (Na2CO3)
- ❌ Thinking a lower pH means more basic — lower pH is more acidic
- ❌ Mixing up brass (copper + zinc) with bronze (copper + tin)
🏆 Exam Tips
- ✅ Blue litmus turns red in acid; red litmus turns blue in base
- ✅ Aluminium is the most abundant metal, oxygen the most abundant element, in the Earth's crust
📌 Summary
- Atom: protons + neutrons in nucleus, electrons around; atomic number = protons
- Mendeleev = Father of Periodic Table; Hydrogen lightest element
- Acids pH below 7 (blue-to-red litmus); bases pH above 7 (red-to-blue); water neutral at 7
- Mercury = only liquid metal; Brass = Cu+Zn, Bronze = Cu+Sn, Steel = Fe+C