Atoms and Molecules Chapter class 9 All types of sum
Answers
Answer:
Law of conservation of mass: Mass can neither be created nor destroyed in a chemical reaction. e.g., A + B → C + D Reactants → Products Mass of reactants = Mass of products
2. Law of constant proportion: In a chemical substance the elements are always present in definite proportions by mass.
E.g., in water, the ratio of the mass of hydrogen to the mass of oxygen is always 1 : 8 respectively.
These laws lacked explanation. Hence, John Dalton gave his theory about the matter. He said that the smallest particle of matter is called ‘atom’.
Explanation:
Dalton’s Atomic Theory
Every matter is made up of very small or tiny particles called atoms.
Atoms are not divisible and cannot be created or destroyed in a chemical reaction.
All atoms of a given element are same in size, mass and chemical properties.
Atoms of different elements are different in size, mass and chemical properties.
Atoms combine in the ratio of a small whole number to form compounds.
The relative number and kinds of atoms are constant in a given compound.
Atom
Atoms are the smallest particles of an element which can take part in a chemical reaction.
Size of an atom: Atomic radius is measured in nanometres.
Symbols of atoms:
(a) Symbols for some elements as proposed by Dalton: