Structure of Atom: Class 9th & NTSE – 01




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1. INTRODUCTION
(i) The idea of tiniest unit of matter (Anu and Parmanu) was propounded by maharishi Kanad in Vedic period in our country.
(ii) Democritus, a Greek philosopher also proposed that matter is made up of extremely small particles, the “atom”. The name atom comes from Greek language.
(iii) John Dalton in 1808 published theory of atom assuming that atoms are the ultimate indivisible particles of matter.
(iv) Later the works f William Crookes (1878), J.J. Thomson (1897) and Goldstein proved that atom of any element contains smaller particles which are either positively charged or negatively charged.
(v) Work of Rutherford and Neil Bohr confirmed that an atom consists of three subatomic particles that are electrons, protons and neutrons.
(vi) It has been established that the central core of an atom consists of protons and neutrons and is commonly called nucleus. The electrons revolve around the nucleus.
(vii) The atom as a whole is electrically neutral as the number of protons in it, is equal to the number of electrons.
The smallest indivisible particle or unit of an element is called an atom, which can take part in a chemical reaction and may or may not exist independently.
An element is a pure substance which cannot be subdivided into two or more new substances by any means.
The word “ATOM” is given by “John Dalton”.

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