Formula - Compound Ki "Recipe" 📝
Ek chemical formula batata hai ki kisi compound (yaugik) mein kaunse elements hain aur kitne-kitne atoms hain. Jaise H₂O batata hai: 2 hydrogen + 1 oxygen. Ye ek chhoti si "recipe" hai jise duniya ka koi bhi scientist padh sakta hai.
Formula likhne ke liye humein sirf ek cheez chahiye - valency (jo humne pichhle chapter mein padhi). Chaliye step-by-step method seekhein.
📋 Common Valencies (Yaad Rakhne Wali)
| Valency 1 | Valency 2 | Valency 3 |
|---|---|---|
| Na, K, H, Ag, Cl, Br, OH⁻, NO₃⁻ | Mg, Ca, Zn, Cu, O, S, CO₃²⁻, SO₄²⁻ | Al, Fe(III), N, PO₄³⁻ |
✂️ Criss-Cross Method - 4 Steps
- Dono elements ke symbols likho - pehle metal (dhaatu)/positive (cation), phir non-metal (adhaatu)/negative (anion).
- Har ek ke upar/neeche uski valency likho.
- Criss-cross karo - yaani ek ki valency ko doosre ke neeche subscript banakar likho.
- Agar dono numbers mein common factor ho toh simplify karo. (Aur subscript 1 ho toh likhte nahi.)
🧮 Solved Examples - Simple Compounds
✔ Example 1 - Sodium Chloride:
Na (valency 1), Cl (valency 1) → criss-cross → Na₁Cl₁ → subscript 1 nahi likhte → NaCl.
✔ Example 2 - Magnesium Chloride:
Mg (valency 2), Cl (valency 1) → criss-cross → Mg₁Cl₂ → MgCl₂.
✔ Example 3 - Aluminium Oxide:
Al (valency 3), O (valency 2) → criss-cross → Al₂O₃.
✔ Example 4 - Calcium Oxide (SIMPLIFY karna zaroori!):
Ca (valency 2), O (valency 2) → criss-cross → Ca₂O₂ → dono mein common factor 2 hai → divide karo → CaO. (Ca₂O₂ likhna galat hoga!)
🔶 Polyatomic Ions Ke Saath (Brackets Ka Rule)
📌 Bracket ka rule: Agar polyatomic ion (jaise OH, SO₄, NO₃) ka subscript 1 se zyada aa raha ho, toh use bracket ( ) mein rakho. Agar subscript 1 ho, toh bracket ki zaroorat nahi.
✔ Example 5 - Calcium Hydroxide:
Ca (valency 2), OH (valency 1) → criss-cross → Ca₁(OH)₂ → Ca(OH)₂.
(OH ka subscript 2 hai, isliye bracket lagaya.)
✔ Example 6 - Sodium Carbonate:
Na (valency 1), CO₃ (valency 2) → criss-cross → Na₂(CO₃)₁ → CO₃ ka subscript 1 hai toh bracket nahi chahiye → Na₂CO₃.
✔ Example 7 - Aluminium Sulphate:
Al (valency 3), SO₄ (valency 2) → criss-cross → Al₂(SO₄)₃ → Al₂(SO₄)₃.
✔ Example 8 - Ammonium Sulphate:
NH₄ (valency 1), SO₄ (valency 2) → criss-cross → (NH₄)₂SO₄ → (NH₄)₂SO₄.
(NH₄ ka subscript 2 hai, isliye usko bracket mein rakha.)
Do elements chuno aur criss-cross se formula banta hua khud dekho - steps ke saath!
Open Builder →📊 Zyada Use Hone Wale Formulae
| Compound | Formula | Compound | Formula |
|---|---|---|---|
| Paani | H₂O | Namak | NaCl |
| Carbon dioxide | CO₂ | Chuna (Calcium oxide) | CaO |
| Ammonia | NH₃ | Calcium hydroxide | Ca(OH)₂ |
| Methane | CH₄ | Sodium hydroxide | NaOH |
| Sulphuric acid | H₂SO₄ | Calcium carbonate | CaCO₃ |
✏️ Khud Try Karo (Practice)
Q. In compounds ke formula likho (answers neeche):
- Potassium chloride (K = 1, Cl = 1)
- Magnesium oxide (Mg = 2, O = 2)
- Aluminium chloride (Al = 3, Cl = 1)
- Sodium sulphate (Na = 1, SO₄ = 2)
Answers: 1) KCl 2) MgO (Mg₂O₂ ko simplify kiya) 3) AlCl₃ 4) Na₂SO₄
🧠 Chalo Test Karein! (Quick Quiz)
Apne aap ko check karo 👇
📌 Aage Kya? (Coming Next)
Ab jab formula likhna aa gaya, toh hum molecular mass aur formula unit mass nikaalna seekhenge - bahut saare solved examples ke saath.