The word ‘atom’ has been derived from the Greek word ‘a-tomio’ which means ‘uncutable’ or
It is the basic unit of an element.
It is a form of matter which cannot be further broken down using any chemical changes.
Nucleus is the very dense region consisting of protons and neutrons at the center of an atom.
Atom is made up of three types of sub-atomic particles; these are electrons, protons and neutrons.
Properties Electron (-1e0) Proton (1p1) Neutron (0n1)
J. J. Thomson in Ernest Rutherford in James Chadwick in
1897 1920 1932
Symbol e p n
Position or located Outside the nucleus Inside the nucleus Inside the nucleus
Electric Charge −1 e or +1 e or 0 e or
−1.6 × 10−19 C 1.6 × 10−19 C 0 C (No Charge)
Mass 9.1 × 10−31 kg or 1.672 × 10−27 kg or 1.674 × 10−17 kg or
5.4 × 10−4 u 1.00727 u 1.00867 u
Cathode Rays and Anode Rays through minutely thin gold foils and
detecting them using screens coated with
For details about cathode and anode rays, zinc sulfide. He found that although the
Please Check ATOMIC AND NUCLEAR vast majority of particles passed straight
PHYSICS in Physics. through the foil approximately 1 in 8000
were deflected leading him to his theory
Rutherford’s Atomic Model
that most of the atom was made up of
This model describes the structure of "empty space".
atoms proposed (1911) by Ernest
Atomic or Chemical Symbol
It described the atom as a tiny, dense, The names of elements have been chosen
positively charged core called a nucleus, for a variety of reasons over the course of
in which nearly all the mass is human and chemical history. It is
concentrated, around which the light, represented by a unique chemical symbol,
negative constituents, called electrons, X.
circulate at some distance, much like The atomic symbol is used to identify the
planets revolving around the Sun. element to which an atom belongs and the
Gold foil experiment : This experiment number of electrons, protons and neutrons
involved the firing of radioactive particles it contains. As noted above, every neutral