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 - 8
Important Formulae
The following are the most important formulae and relations from Chapter 8: Journey Inside the Atom. Learn these thoroughly for examinations and numerical problems.
| Formula | Meaning |
|---|---|
| Atomic Number (Z) = Number of Protons (p) | The atomic number of an element is equal to the number of protons present in its nucleus. |
| For a Neutral Atom: Number of Electrons (e) = Number of Protons (p) |
A neutral atom has equal numbers of protons and electrons. |
| Mass Number (A) = Number of Protons + Number of Neutrons | The mass number is the total number of nucleons present in the nucleus. |
| A = p + n | Short form of the Mass Number formula. |
| Number of Neutrons (n) = Mass Number − Atomic Number | Used to calculate the number of neutrons present in an atom. |
| n = A − Z | Short form of the neutron formula. |
| Maximum Electrons in nth Shell = 2n² | Bohr–Bury rule used to calculate the maximum number of electrons in any shell. |
Bohr–Bury Rule
| Shell | Value of n | Maximum Electrons (2n²) |
|---|---|---|
| K | 1 | 2 |
| L | 2 | 8 |
| M | 3 | 18 |
| N | 4 | 32 |
Quick Formula Sheet
| Concept | Formula |
|---|---|
| Atomic Number | Z = p |
| Mass Number | A = p + n |
| Neutrons | n = A − Z |
| Electrons (Neutral Atom) | e = p = Z |
| Maximum Electrons in Shell | 2n² |
Exam Formula Box
Atomic Number = Number of Protons
Mass Number = Protons + Neutrons
Neutrons = Mass Number − Atomic Number
Electrons (Neutral Atom) = Protons
Maximum Electrons in nth Shell = 2n²
Remember
- ✔ Atomic Number is represented by Z.
- ✔ Mass Number is represented by A.
- ✔ Number of nucleons = Protons + Neutrons.
- ✔ A neutral atom always has equal numbers of protons and electrons.
- ✔ The outermost shell can have a maximum of 8 electrons (except the K-shell, which can have only 2 electrons).