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Quantum Theory

Why do s, p, d, f, ... ? Why not a, b, c, d,...? Why s, p, d, f, ... ? Why not a, b, c, d,...? An atomic orbital is a mathematical function that can be used to calculate the probability of finding any electron of an atom in any specific region around the atom’s nucleus. These atomic orbitals have spherical, dumb‐bell, double dumb‐bell and complex shapes. The names (s, p, d, f, g, h,...) of these orbitals are derived from the characteristics of their spectroscopic lines: sharp (s), principal (p), diffuse (d), and fundamental (f), the rest being named in alphabetical order. The sharp and diffuse series are so named because of the appearance of the sharp and diffused spectral lines. The principal lines are so called because they are most intense lines. Fundamental lines have the comparable frequencies with frequencies of fundamental lines in hydrogen atomic spectra.

Learning Objectives

After completing the topic, the student will be able to:

  • Identify that matter and energy are not different entities and both light(energy) and matter have dual nature.
  • Calculate the wavelength and momentum of moving bodies using de Broglie wave equation.
  • Discuss the diffraction and scattering experiments by Davisson and Germer that prove the wave nature of matter.
  • Understand the uncertainty phenomenon and how it limits our knowledge of properties of quantum particles.
  • Recognize the significance of probability density,
    | Ψ(x) |2.
  • Depict the electron location within an atom by analyzing electron density diagrams and radial probability distribution plots.
  • Describe the size, shape and orientation of an atomic orbital by using quantum numbers.
Morning rays Morning rays Rays of light through the trees on a cool morning.

First thing we can say about light is that it is something that enables us to see. But what is light? We know that during the day the primary source of the light is the Sun, and the secondary source is the brightness of the Sky. Other common sources are flames, white‐hot filaments in light bulbs and glowing gas in glass tubes.

Light is a form of energy, which enables us to see objects from which it comes. We detect light by our eye, which is an optical instrument provided to us by nature. Light can be transmitted from one place to another at finite velocity. Light energy originates somewhere within an atom and ends its existence when it enters another atom or molecule. All light originates from the accelerated motion of electric charges.

Visible light region of electromagnetic spectrum Visible light region of electromagnetic spectrum The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 700 nm.
Theories of Light

Light is an electromagnetic phenomenon; visible light is a tiny part of a larger electromagnetic spectrum of radiation ranging from cosmic rays to radio waves. Knowledge of the nature of light and the emission and absorption processes are very important.

Two complimentary theories have been proposed to explain how light behaves and the form by which it travels.

  1. Particle theory: Release of small amount of energy as a photon when an atom is excited.
  2. Wave theory: Radiant energy travels as a wave from one point to another. Waves have electrical and magnetic properties (electromagnetic variations).

The scientific study of the behaviour of light covers reflection, refraction, polarization, diffraction of light as it passes by the edge of an opaque object and interference patterns resulting from diffraction. Newton proposed that light consists of small particles, with which he could explain the phenomenon of reflection, refraction and splitting of sunlight into a rainbow by a prism. Christian Huygens proposed wave theory of light and demonstrated how waves might interfere to form a wave front, propagating in a straight line.

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