CBSE · Class 9

Chemistry Formulas — Class 9

Key formulas and concepts for CBSE Class 9 Chemistry — matter, atoms, molecules, structure of atom and chemical reactions.

6 chapters26+ formulasCBSE 2026–27

Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6

⚠

For reference only. Always verify formulas and information against your official NCERT textbooks or board-prescribed materials before use in exams. Learnizo does not guarantee absolute accuracy.

Ch 1.Matter in Our Surroundings

Formula / Relation	Expression	Note
Density	Density = Mass / Volume (ρ = m/V)	SI unit: kg/m³; common unit: g/cm³; 1 g/cm³ = 1000 kg/m³
Temperature conversions	K = °C + 273 (or + 273.15 precisely)	0°C = 273 K; 100°C = 373 K; Kelvin is always positive
Celsius to Fahrenheit	°F = (°C × 9/5) + 32	Water freezes at 0°C = 32°F; boils at 100°C = 212°F

Ch 2.Is Matter Around Us Pure? (Mixtures and Solutions)

Formula / Relation	Expression	Note
Mass percentage of solute	Mass% = (Mass of solute / Mass of solution) × 100	Mass of solution = mass of solute + mass of solvent
Volume percentage	Volume% = (Volume of solute / Volume of solution) × 100	Used for liquid in liquid solutions (e.g., ethanol in water)

Ch 3.Atoms and Molecules

Formula / Relation	Expression	Note
Mole concept	1 mole = 6.022 × 10²³ particles (Avogadro's number, Nₐ)	1 mole of any substance contains 6.022 × 10²³ entities (atoms, molecules, ions)
Molar mass	Molar mass = Mass in grams of 1 mole of substance	Numerically equal to relative atomic/molecular mass but in g/mol
Number of moles	n = Given mass (g) / Molar mass (g/mol)	Also: n = Number of particles / Nₐ
Number of particles	N = n × Nₐ = n × 6.022 × 10²³	N = total number of atoms/molecules/ions
Mass from moles	Mass = n × Molar mass	Reverse of the mole calculation
Relative molecular mass (Mr)	Mr = Sum of relative atomic masses of all atoms in one molecule	Example: H₂O → Mr = 2(1) + 16 = 18

Ch 4.Structure of the Atom

Formula / Relation	Expression	Note
Atomic number (Z)	Z = Number of protons = Number of electrons (in neutral atom)	Also called the proton number; defines the element
Mass number (A)	A = Number of protons + Number of neutrons = Z + N	N = number of neutrons; A is also called atomic mass number
Number of neutrons	N = A − Z	Neutrons = Mass number − Atomic number
Bohr's electron shell capacity	Maximum electrons in nth shell = 2n²	Shell 1 (K): max 2; Shell 2 (L): max 8; Shell 3 (M): max 18; Shell 4 (N): max 32
Valence electrons	Valence electrons = electrons in outermost shell	Determine chemical properties and bonding; for main group elements, same as group number

Ch 5.Common Chemical Formulae (Class 9 Level)

Formula / Relation	Expression	Note
Water	H₂O	2 hydrogen + 1 oxygen; molecular mass = 18 u
Carbon dioxide	CO₂	1 carbon + 2 oxygen; molecular mass = 44 u
Sodium chloride (common salt)	NaCl	Na (sodium) + Cl (chlorine); formula mass = 58.5 u
Ammonia	NH₃	1 nitrogen + 3 hydrogen; molecular mass = 17 u
Sulphuric acid	H₂SO₄	2H + S + 4O; molecular mass = 98 u
Hydrochloric acid	HCl	1 hydrogen + 1 chlorine; molecular mass = 36.5 u
Sodium hydroxide	NaOH	Na + O + H; formula mass = 40 u
Glucose	C₆H₁₂O₆	6 carbon + 12 hydrogen + 6 oxygen; molecular mass = 180 u

Ch 6.Law of Chemical Combination

Formula / Relation	Expression	Note
Law of Conservation of Mass	Mass of reactants = Mass of products	Antoine Lavoisier; in a chemical reaction, total mass is conserved
Law of Constant Proportions	Elements in a compound are always in a fixed mass ratio	Proust's Law; H₂O always has H:O mass ratio = 1:8

Frequently Asked Questions

What is the mole concept in Class 9 Chemistry?

The mole concept is a counting unit for particles. 1 mole = 6.022 × 10²³ particles (Avogadro's number). The molar mass of a substance in grams numerically equals its relative atomic/molecular mass in unified atomic mass units (u). For example, the molar mass of water (H₂O) is 18 g/mol — so 18 g of water contains 6.022 × 10²³ water molecules. The key formula is n = mass / molar mass.

What is the difference between atomic number and mass number?

Atomic number (Z) = number of protons = number of electrons in a neutral atom. It uniquely identifies an element — all atoms of the same element have the same Z. Mass number (A) = number of protons + number of neutrons. Neutrons = A − Z. Isotopes have the same Z but different A (different number of neutrons). Example: Carbon-12 has Z=6, A=12, neutrons=6. Carbon-14 has Z=6, A=14, neutrons=8.

Related resources

Class 9 Chemistry coaching on Learnizo

Expert Class 9 Science tutors covering Chemistry chapters — atoms, molecules, matter and structure of atom.

Find a Science Tutor