1st Year Chemistry Chapter 5 Notes

• Discovery of Electron (Cathode Rays)
• Value of voltage for production of cathode rays
• The colour of the glow or the fluorescence produced on the walls of the glass tube depends upon the composition of glass.
• Describe the Properties of Cathode Rays
• Historical Background of Discovery of Proton (Positive Rays)
• Reason for the Production of Positive Rays
• Describe the Properties of Positive Rays
• Historical Background of Discovery of Neutron
• Describe the Properties of Neutron
• Experiment of Rutherford’s Model of Atom:  In 1911, Lord Rutherford performed a classic experiment. Experiment He studied the scattering of high speed α-particles which were emitted from a radioactive metal (radium or polonium). Setting • A beam of α-particles was directed onto a gold foil of 0.00004 cm thickness as target through a pin-hole in lead plate. • A photographic plate or a screen coated with zinc sulphide was used as a detector. • Whenever, an α-particle struck the screen, flash of light was produced at that point. It was observed that most of the particles went through the foil undeflected. Some were deflected at fairly large angles and a few were deflected backward. Proposals • Rutherford proposed that the rebounding particles must have collided with the central heavy portion of the atom which he called as nucleus. • On the basis of these experimental observations, Rutherford proposed the planetary model (similar to the solar system) for an atom in which a tiny nucleus is surrounded by an appropriate number of electrons. • Atom as a whole being neutral, therefore, the nucleus must be having the same number of protons as there are number of electrons surrounding it.
• Measurement of e/m Value of Electron with apparatus and working
• Measurement of Charge on Electron-Millikan’s Oil Drop Method
• Define the Quantum numbers 
• Spin Quantum Number: In 1925, Goudsmit and Uhlenbech suggested that an electron while moving in an orbital around the nucleus also rotates about its own axis either in a clockwise or anti-clockwise direction. This is also called self-rotation. Opposite magnetic fields are generated by the clockwise and anti-clockwise spins of electrons. Background Alkali metals have one electron in their outermost shell. Their emission spectra are observed by means of high resolving power spectrometer and each line in the spectrum is found to consist of pair of lines. This is called doublet line structure. Lines of doublet line structure are widely separated from each other. This spin motion is responsible for doublet line structure in the spectrum. 
• 1. Write any four properties of cathode rays.     2. How did Rutherford discover the nucleus of atom? 
• 3. Give properties of neutron in detail.          4. Write down the experiment how neutron was discovered.
• 5. Describe J.J Thomson’s experiment for determining e/m value of electron.
• 6. Describe Millikan’s oil drop method for the measurement of charge on electron.
• 7. Write four defects of Bohr’s atomic model.
• 8. Derive the formula for calculating the energy of an electron in nth orbit using Bohr’s model.
• 9. Derive an expression to determine the radius of an orbit using Bohr Model.
• 10. Define Quantum numbers. Discuss briefly Azimuthal quantum number/principal quantum number/magnetic quantum number and spin quantum number.