Chapter at a glance
The laws of chemical combination, Dalton’s atomic theory, how atoms bond (ionic and covalent), writing chemical formulae, and calculating molecular and formula unit masses. The textbook title is ‘Atomic Foundations of Matter’.
What this chapter covers
- 9.1 Law of Conservation of Mass
- 9.2 Law of Constant Proportions
- 9.3 Dalton’s Atomic Theory
- 9.4 How Atoms Combine?
- 9.5 Writing Chemical Formulae
- 9.6 Properties of Ionic and Covalent Compounds
- 9.7 Molecular Mass of Covalent Compounds
- 9.8 Formula Unit Mass of Ionic Compounds
Key points
- Mass is neither created nor destroyed in a chemical reaction.
- A compound always has the same elements in a fixed ratio by mass.
- Covalent bonds share electrons; ionic bonds transfer them, forming cations and anions.
- Molecular mass is the sum of the atomic masses in a molecule; formula unit mass is the same for ionic compounds.
Read the NCERT chapter
Read this chapter in the official NCERT textbook Exploration (2026-27 edition) for free on ncert.nic.in.
Source: NCERT, Exploration, Grade 9 (2026-27). NCERT chapter PDF. Spotted a mistake? Email edura.class9.yt@gmail.com. Last updated 11 October 2026.