100 Short Q&A for Atomic Structure (Class 11 NCERT) Part 1: Fundamental Particles and Early Models Q. No. Question Answer 1 Who discovered the electron? J. J. Thomson (using Cathode Ray Tube). 2 Who discovered the proton? E. Goldstein (using Canal Rays). 3 Who discovered the neutron? James Chadwick. 4 What is the charge-to-mass ratio (e/m) of an electron? 1.758820×1011 C/kg. 5 What is the charge of an electron? −1.602×10−19 Coulombs (Millikan's Oil Drop method). 6 What is the mass of a proton (in kg)? Approximately 1.672×10−27 kg. 7 What is an α-particle? A doubly positively charged helium nucleus (4He2+). 8 What did Thomson's model of the atom propose? A "Plum Pudding" or "Watermelon" model with embedded electrons. 9 What was the major observation of Rutherford's α-scattering experiment? Most α-particles passed straight through the gold foil. 10 What is the dense, central part of an atom called? The Nucleus. 11 What did Rutherford's model fail t...

  Atomic terms a) Atomic Number (Z): The atomic number of an element is the number of protons contained in the nucleus of the atom of that element. b) Nucleons: Protons and neutrons are present in a nucleus. So, these fundamental particles are collectively known as nucleons. c) Mass Number (A): The total number of protons and neutrons i.e,  the number of nucleons present in the nucleus is called the mass number of the element. d) Nuclide: Various species of atoms in general. A nuclide has specific values of atomic number and mass number. IUPAC notation of an atom (nuclide) Let X be the symbol of the element. Its atomic number be Z and mass number be A. Then  the element can be represented as   e) Isotopes:   Atoms of the element with same atomic number but different mass number e.g. 1 H 1 , 1 H 2 , 1 H 3 . There are three isotopes of hydrogen. f) Isobars: Atoms having the same mass number but different atomic numbers, e.g. 15 P 32  and 16 S ...