SCIENCE IMPORTANT FORMULAE CLASS - 9
Important Formulae for class 9 science
Updated for new syllabus - 2026
Class 9 science Important Formulae
The Important Science Formulae section at Saraswat Academy provides a complete collection of chapter-wise scientific formulas based on the latest CBSE Syllabus 2026–27. These formulas are carefully selected from the NCERT textbooks and presented in a simple, easy-to-understand format for quick learning and revision. They help students strengthen their conceptual understanding, solve numerical problems accurately, and improve problem-solving speed in Physics, Chemistry, and other formula-based topics. Regular practice of these formulas is essential for homework, class tests, unit tests, practical examinations, half-yearly examinations, annual examinations, and CBSE board examinations. This page serves as a quick revision resource, enabling students to recall important formulas confidently and perform better in both school and competitive examinations.
Regular revision of scientific formulas helps students strengthen conceptual understanding, improve numerical problem-solving skills, and reduce errors in calculations during examinations. Whether you are preparing for school assessments, practical examinations, or CBSE board exams, these chapter-wise science formula sheets provide a quick and effective revision resource. Students are encouraged to practise these formulas alongside NCERT questions, exemplar problems, practical-based questions, competency-based questions, and previous years' board questions to develop scientific reasoning, enhance accuracy, and achieve excellent marks in Science.
Important Formulae: Science Class - 9
Chapter - 9
🧮 Important Formulae
Although Chapter 9: Atomic Foundations of Matter is mainly conceptual, a few important formulae and relations are frequently used in numerical problems and while writing chemical formulae.
| Formula / Relation | Meaning |
|---|---|
| Mass of Reactants = Mass of Products | According to the Law of Conservation of Mass, the total mass remains constant during a chemical reaction. |
| Total Positive Charge = Total Negative Charge | In an ionic compound, the total positive and negative charges must be equal. |
| Chemical Formula = Crossover of Valencies | Write the symbols of the ions/elements and interchange their valencies to obtain the chemical formula. |
Writing Chemical Formula (Crossover Rule)
| Compound | Valencies | Formula |
|---|---|---|
| Sodium Chloride | Na¹ & Cl¹ | NaCl |
| Magnesium Chloride | Mg² & Cl¹ | MgCl₂ |
| Calcium Oxide | Ca² & O² | CaO |
| Aluminium Oxide | Al³ & O² | Al₂O₃ |
| Calcium Nitride | Ca² & N³ | Ca₃N₂ |
Common Valencies
| Ion / Element | Valency |
|---|---|
| H | 1 |
| Na | 1 |
| K | 1 |
| Cl | 1 |
| O | 2 |
| Mg | 2 |
| Ca | 2 |
| Zn | 2 |
| Al | 3 |
| N | 3 |
Quick Formula Sheet
| Concept | Formula / Rule |
|---|---|
| Law of Conservation of Mass | Mass of Reactants = Mass of Products |
| Ionic Compound | Total (+) Charge = Total (−) Charge |
| Chemical Formula | Use the Crossover Method |
🎯 Exam Formula Box
Mass of Reactants = Mass of Products
Total Positive Charge = Total Negative Charge
Chemical Formula = Crossover of Valencies
📌 Remember
- ✔ Always apply the Law of Conservation of Mass while solving numerical problems.
- ✔ The total positive and negative charges in an ionic compound must always be equal.
- ✔ Reduce the formula to the simplest whole-number ratio after applying the crossover method.
- ✔ Do not write the valency number 1 in the final chemical formula (e.g., write NaCl, not Na₁Cl₁).
- ✔ Learn the common valencies of frequently used elements and ions for quick formula writing.