Learn about the basics of atoms and molecules, their properties, laws, and types of bonds. Download PDF notes and watch video summary of Chapter 3 of CBSE Class 9 Science textbook. The atomic mass of an element is multiplied by the number of atoms in the molecule, and the masses of all the elements in the molecule are added to get the molecule's mass. er of atom atomicity. For example, each of the molecules of hydrogen, nitrogen, oxygen, chlorine, iodine, and bromine has two atoms, and hence they all have two atomicity each. CBSE Class 9 Notes Science Chapter 3 - Atoms And Molecules Ancient Indian philosopher Maharishi Kanad proposed that matter is divisible until the tiniest particles, called "Parmanu." Similarly, Greek philosopher Democritus introduced the concept of indivisible particles, "atoms." Atoms are indivisible particles, which can neither be created nor destroyed in a chemical reaction. The atoms of a given element are identical in mass and chemical properties. Atoms of different elements have different masses and chemical properties. Atoms combine in the ratio of small whole numbers to form compounds.
