Structure of Atom Nootan Solutions ISC Chemistry Class-11 Ch-2

Structure of Atom Nootan Solutions ISC Chemistry Class-11 Ch-2 Review Numerical Questions . Step by step Solutions of Dr. HC Srisvastava ISC Chemistry Class-11 Nageen Prakashan Numerical review Questions. Visit official Website CISCE for detail information about ISC Board Class-11 Chemistry

Structure of Atom Nootan Solutions ISC Chemistry Class-11 Ch-2

Class: 11
Subject: Chemistry
Chapter 2: Structure of Atom
Board ISC
Writer  Dr. HC Srisvastava
Publications Nageen Prakashan
Book Name Nootan
Topics Solved review Numerical questions of page 97-164

Discovery of Electron-Discharge Tube Experiment

In 1879, William Crooks studied the conduction of electricity through gases at low pressure. He performed the experiment in a discharge tube which is a cylindrical hard glass tube about 60 cm in length. It is sealed at both the ends and fitted with two metal electrodes. The electrical discharge through the gases could be observed only at very low pressures and at very high voltages.

The pressure of different gases could be adjusted by evacuation. When sufficiently high voltage is applied across the electrodes, current starts flowing through a stream of particles moving in the tube from the negative electrode (cathode) to the positive electrode (anode). These were called cathode rays or cathode ray particles.

Properties of Cathode Rays

(i) Cathode rays travel in straight line.

(ii) Cathode rays start from cathode and move towards the anode.

(iii) These rays themselves are not visible but their behaviour can be observed with the help of certain kind of materials (fluorescent or phosphorescent) which glow when hit by them.

Discovery of Proton-Anode Rays

In 1886, Goldstein modified the discharge tube by using a perforated cathode. On reducing the pressure, he observed a new type of luminous rays passing through the holes or perforations of the cathode and moving in a direction opposite to the cathode rays. These rays were named as positive rays or anode rays or as canal rays. Anode rays are not emitted from the anode but from a space between anode and cathode.

Properties of Anode Rays

(i) The value of positive charge (e) on the particles constituting anode rays depends upon the nature of the gas in the discharge tube.

(ii) The charge to mass ratio of the particles is found to depend on the gas from which these originate.

(iii) Some of the positively charged particles carry a multiple of the fundamental unit of electrical charge.


The smallest and lightest positive ion was obtained from hydrogen and was called proton. Mass of proton = 1.676 x 10-27 kg
Charge on a proton = (+) 1.602 x 10-19 C


It is a neutral particle. It was discovered by Chadwick (1932). By the bombardment of thin sheets of beryllium with fast moving a-particles he observed • that highly penetrating rays consist of neutral particles which were named neutrons.

 Atomic Number

The number of protons present in the nucleus is equal to the atomic number (z). For example, the number of protons in the hydrogen nucleus is 1, in sodium atom it is 11, therefore, their atomic numbers are 1 and 11. In order to keep the electrical neutrality, the number of electrons in an atom is equal to the number of protons (atomic number, z). For example, number of electrons in hydrogen atom and sodium atom are 1 and 11 respectively.

Atomic Number (z) = Number of protons in the nucleus of an atom.
= Number of electrons in a neutral atom.

Developments Leading to the Bohr’s Model of Atom

Two developments played a major role in the formulation of Bohr’s model of atom. These were:

(i) Dual character of the electromagnetic radiation which means that radiations possess both wave like and particle like properties.

(ii) Experimental results regarding atomic spectra which can be explained only by assuming quantized electronic energy levels in atoms.

Quantum Mechanical Model of Atom

Quantum mechanics: Quantum mechanics is a theoretical science that deals with the study of the motions of the microscopic objects that have both observable wave like and particle like properties.

Important Features of Quantum Mechanical Model of Atom

(i) The energy of electrons in atom is quantized i.e., can only have certain values.

(ii) The existence of quantized electronic energy level is a direct result of the wave like properties of electrons.

(iii) Both the exact position and exact velocity of an electron in an atom cannot be determined simultaneously.

Structure of Atom Nootan Solutions

ISC Chemistry Class-11 Chapter-2 Review Questions

Structure of Atom Nootan Solutions

ISC Chemistry Class-11 Chapter-2 review Numerical Solutions

— End of Structure of Atom Nootan Solutions :–

Return to  – Nootan Solutions for ISC Chemistry Class-11 Nageen Prakashan


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