Atomic Structure - Chapter 1 - ( Chemistry ) - Important for WBCS, SSC, IBPS and other exams


Chapter 1 : Atomic Structure
Introduction : The Word Atom comes from Greek Word atomos. The concept of Atom first propounded by Indian Philosopher Kanad who said that every matter consist of particles(Paramanu – means very small) which can not be broken further. But modern Atomic theory proved that atoms are divisible and consist of a central core with negatively charged electrons revolving round the core, the core consists of positively charged protons and neutrons. The core is called the nucleus of an atom.
All the important information about Sub-Atomic Particles below :
with Mass(gm)
Eletric Charge Unit
Important Information

Mass : 9.11 x 10-28


4.8 x 10-19

1.602 x 10-19

Its a Negative charged Particle in Atom around the nucleus. The first Precise measurement of charge on electron was made by Robert A. Milikan by oil drop experiment.
Discovered by : J.J. Thompson

Mass : 1.672 x 10-24


4.8 x 10-19

1.602 x 10-19


Like electron, proton is a positively charged particle. Named by : Rutherford.
And Discovered by : Eurene Goldstein

Mass : 1.675 x 10-24





Discovered by : J. Chadwick.
He bombared beryllium with a stream of alpha particle. He observed that penetrating radiations  were produced which were not affected by electric and magnetic fields. It consists neutral particles, he named it Neutrons.

Atomic Model :
Rutherford’s Atomic Model : Rutherford atomic model, also called nuclear atom or planetary model of the atom, description of the structure of atoms proposed (1911) by the New Zealand-born physicist Ernest Rutherford. The model described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun. Bohr further enriched this model.
To know More about Rutherford’s Atomic Model : Visit Encyclopeadia Britanicca
Bohr’s Atomic Model : Electrons are revolving around the nucleus in fixed orbits of definite energy called energy level. As long as electrons rotates in one of the fisex orbits it neither loses or absorbs energy. Summerfield further enriched this model.
Summerfield’s Atomic Model : Summerfield suggested that orbits can be elliptical shape and in that case nucleus is placed in one of its focii.
Shells Structure of Atom
Shell No
Maximum Electron number (2n2)
2 x 12 = 2
2 x 22 = 8
2 x 32 = 18
2 x 42 = 32

Atomic Weight : The Atomic weight is the weight of one atom of an element in comparison with the 1/12th weight of an atom of carbon – 12 atom. It is Unitless.
Mole : Molecular weight of a molecule expressed in gram is called gm mole or mole. The number of particles in one mole of a substant is constant and value is 6.023 x 1023 . It is knowm as Avogadro’s number.
Atomic Number : The atomic number is defined as the number of protons or the number of electrons for a neutral atom in the atom.
Mass Number : The Total number of the protons and neutrons present in the nucleus of an atom is known as the mass number of the atom.
Isotope : The atom of the same elements having different masses are called isotopes. Example of isotopes : Hydrogen – protium , deuterium, tritium, chlorine...
Isobars : There are some cases where mass number is same but elements are different, the atomic number are the different. Such pairs of element are known as Isobars. Example : Argon (18Ar40) and (20Ca40).
Isotones : Same number of neutrons but different mass number and atomic number, such pairs are called Isotones. Example : 15P31 and 14Si30 .
Note :

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1 comment:

  1. Thank you . very effective . please upload chapter 2.


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