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  Pauli’s Exclusion Principle ❒  The nature of an electron, its position and energy, is fully implied only by mentioning the values of four quantum numbers ascribed to it. ❒ Each electron is, therefore, fully characterised by a set of four quantum numbers (n) – giving the size of electron …

  Quantum Numbers ❒ Bohr’s electronic energy shells or levels, designated as Principal Quantum Numbers (n), could hardly explain the hydrogen spectrum adequately. Spectra of other elements that are quite complex, also remained unexplained by this concept. ❒ Many single lines of the spectra are found to consist of a …

  Schrödinger’s Wave Equation ❒ In order to provide sense and meaning to the probability approach, Schrödinger derived an equation known after his name as Schrödinger’s Wave Equation.  ❒ Calculation of the probability of finding the electron at various points in an atom was the main problem before Schrödinger.    ❒ His …

  Heisenberg’s uncertainty Principle ❒One of the most important consequences of the dual nature of matter is the uncertainty principle developed by Werner Heisenberg in 1927. ❒ This principle is an important feature of wave mechanics and discusses the relationship between a pair of conjugate properties (those properties that are …

    1. Cathode rays are deflected by_______ (a) electric field only (b) magnetic field only (c) electric and magnetic field (d) none of these Answer. (c) 2. The e/m value for the particles constituting cathode rays is the same regardless of_______ (a) the gas present in cathode rays tube …

  De Broglie’s Equation ❒de Broglie had arrived at his hypothesis with the help of Planck’s Quantum Theory and Einstein’s Theory of Relativity. ❒He derived a relationship between the magnitude of the wavelength associated with the mass (m) of a moving body and its velocity. ❒According to Planck, the photon …

  Zeeman Effect ❒ In 1896 Zeeman discovered that spectral lines are split up into components when the source emitting lines is placed in a strong magnetic field. It is called the Zeeman effect after the name of the discoverer. ❒ The apparatus used to observe Zeeman effect is shown …

   Having known that planetary electrons numerically equal to the atomic number are revolving about the atomic nucleus in closed orbits, the question arises as to how they are arranged in these orbits. Langmuir Scheme ❒ We are indebted to Langmuir for putting forward the first elaborate scheme of the …

  ❒ Rutherford’s nuclear model simply stated that atom had a nucleus and the negative electrons were present outside the nucleus. It did not say anything as to how and where those electrons were arranged. It also could not explain why electrons did not fall into the nucleus due to …

  Photoelectric Effect ❒When a beam of light of sufficiently high frequency is allowed to strike a metal surface in vacuum, electrons are ejected from the metal surface. This phenomenon is known as Photoelectric effect and the ejected electrons Photoelectrons.  ❒For example, when ultraviolet light shines on Cs (or Li, …

  Atomic Spectra ❒When an element in the vapour or the gaseous state is heated in a flame or a discharge tube, the atoms are excited (energised) and emit light radiations of a characteristic colour. The colour of light produced indicates the wavelength of the radiation emitted.       …

  Mosley’s Determination of Atomic number ❒ The discovery that atom has a nucleus that carries a positive charge raised the question : What is the magnitude of the positive charge? This question was answered by Henry Mosley in 1913. ❒ Hitherto atomic number was designated as the ‘position number’ …

  Alpha particles ❒ Alpha particles are shot out from radioactive elements with very high speed. ❒ For example, they come from radium atoms at a speed of 1.5 × 107m/sec. Rutherford identified them to be di-positive helium ions, He2+or 4He2. Thus an alpha particle has 2+ charge and 4 …

Subatomic Particles ❒We have hitherto studied the properties of the three principal fundamental particles of the atom, namely the electron, proton, and neutron. These are summarised in this Table:   ❒Nearly all of the ordinary chemical properties of matter can be examined in terms of atoms consisting of electrons, protons …

Cathode Rays – The discovery of electron ❒The knowledge about the electron was derived as a result of the study of the electric discharge in the discharge tube (J.J. Thomson, 1896).   (1) The discharge tube consists of a glass tube with metal electrodes fused in the walls. (2) Through …