Science
JSUNIL TUTORIAL , SAMASTIPUR, BIHAR
IX CBSE CHAPTR - ATOMS AND MOLECULES
The word atom is derived from the Greek word “Atomos” which means indivisible. John Dalton modelled atoms as hard indivisible spheres.
An Indian philosopher Maharishi Kanad, postulated that if we go on dividing matter (padarth), we shall get smaller and smaller particles. Ultimately, a time will come when we shall come across the smallest particles beyond which further division will not be possible. He named these particles Parmanu.
Ancient Greek philosophers – Democritus and Leucippus suggested that if we go on dividing matter, a stage will come when particles obtained cannot be divided further. Democritus called these indivisible particles atoms (meaning indivisible).
How and why elements combine and what happens when they combine. Antoine L. Lavoisier laid the foundation of chemical sciences by establishing two important laws of chemical combination.
(a) The Law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. (b) The law of constant proportions which is also known as the law of definite proportions was stated by
Proust as “In a chemical substance the elements are always present in definite proportions by mass”.
E.g. In a compound such as water, the ratio of the mass of hydrogen to the mass of oxygen is always 1:8, whatever the source of water. Thus, if 9 g of water is decomposed, 1 g of hydrogen and 8 g of oxygen are always obtained.
According to Dalton‟s atomic theory, all matter, whether an element, a compound or a mixture is composed of small particles called atoms. The postulates of this theory may be stated as follows:
(i) All matter is made of very tiny particles called atoms.
(ii) Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.
(iii) Atoms of a given element are identical in mass and chemical properties.
(iv) Atoms of different elements have different masses
IX CBSE CHAPTR - ATOMS AND MOLECULES
The word atom is derived from the Greek word “Atomos” which means indivisible. John Dalton modelled atoms as hard indivisible spheres.
An Indian philosopher Maharishi Kanad, postulated that if we go on dividing matter (padarth), we shall get smaller and smaller particles. Ultimately, a time will come when we shall come across the smallest particles beyond which further division will not be possible. He named these particles Parmanu.
Ancient Greek philosophers – Democritus and Leucippus suggested that if we go on dividing matter, a stage will come when particles obtained cannot be divided further. Democritus called these indivisible particles atoms (meaning indivisible).
How and why elements combine and what happens when they combine. Antoine L. Lavoisier laid the foundation of chemical sciences by establishing two important laws of chemical combination.
(a) The Law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. (b) The law of constant proportions which is also known as the law of definite proportions was stated by
Proust as “In a chemical substance the elements are always present in definite proportions by mass”.
E.g. In a compound such as water, the ratio of the mass of hydrogen to the mass of oxygen is always 1:8, whatever the source of water. Thus, if 9 g of water is decomposed, 1 g of hydrogen and 8 g of oxygen are always obtained.
According to Dalton‟s atomic theory, all matter, whether an element, a compound or a mixture is composed of small particles called atoms. The postulates of this theory may be stated as follows:
(i) All matter is made of very tiny particles called atoms.
(ii) Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.
(iii) Atoms of a given element are identical in mass and chemical properties.
(iv) Atoms of different elements have different masses