Class 9th Chemistry-Chapter 3 Notes

During a chemical reaction, the sum of the masses of the reactants remains unchanged, his is known as Law of Conservation of Mass.
In a pure chemical compound, elements are always present in a definite proportion by mass.
An atom is the smallest particle of matter/element that can exist independently and retain all its chemical properties.
A molecule is the smallest particle of an element or compound capable of independent existence under ordinary conditions.
Compounds composed of metals and non-metals contain charged species, the species are known as ions.
A group of atoms carrying a charge is known as poly-atomic ion.
The Avogadro constant 6.022 x 10²³ is defined as the number of atoms in exactly 12 g of carbon -12.
The mole is the amount of substance that contains the same number of particles (atoms/ ions/ molecules/ formula units etc.) as there are atoms in exactly 12 g of carbon - 12.
Mass of 1 mole of a substance is called its molar mass.

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