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SCIENCE IMPORTANT FORMULAE CLASS - 9

Important Formulae for class 9 science
Updated for new syllabus - 2026

CBSENCERTFORMULAE

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 2026โ€“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



๐Ÿงฎ 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 Naยน & Clยน NaCl
Magnesium Chloride Mgยฒ & Clยน MgClโ‚‚
Calcium Oxide Caยฒ & Oยฒ CaO
Aluminium Oxide Alยณ & Oยฒ Alโ‚‚Oโ‚ƒ
Calcium Nitride Caยฒ & Nยณ Caโ‚ƒNโ‚‚


Common Valencies

Ion / Element Valency
H1
Na1
K1
Cl1
O2
Mg2
Ca2
Zn2
Al3
N3


Quick Formula Sheet

Concept Formula / Rule
Law of Conservation of Mass Mass of Reactants = Mass of Products
Ionic Compound Total (+) Charge = Total (โˆ’) Charge
Chemical Formula Use the Crossover Method


๐ŸŽฏ Exam Formula Box

Mass of Reactants = Mass of Products

Total Positive Charge = Total Negative Charge

Chemical Formula = Crossover of Valencies



๐Ÿ“Œ Remember

  • โœ” Always apply the Law of Conservation of Mass while solving numerical problems.
  • โœ” The total positive and negative charges in an ionic compound must always be equal.
  • โœ” Reduce the formula to the simplest whole-number ratio after applying the crossover method.
  • โœ” Do not write the valency number 1 in the final chemical formula (e.g., write NaCl, not Naโ‚Clโ‚).
  • โœ” Learn the common valencies of frequently used elements and ions for quick formula writing.