AHA! Chemistry with Prof Bob
  • Home
  • Modules
    • 02 The nature of matter >
      • 0201 Atoms: Building blocks
      • 0202 Classification of matter
    • 05 Chemical reaction, chemical equations >
      • 0500 Overview, preview
      • 0501 Amount of substance, mole
      • 0502 Avogadro constant: How many?
      • 0503 Avogadro constant: Why that number?
      • 0504 Chemical formulas: What do they mean?
      • 0505 What can equations tell us?
      • 0506 Limiting reactants
    • 09 Solutions >
      • 0901 What is a solution?
      • 0902 Miscibility of liquids
      • 0903 Like dissolves like?
      • 0905 Dissolution of ionic salts in water
      • 0906 Can we predict solubilities of salts?
      • 0907 Solution concentration
      • 0908 Chemical species, speciation
      • 0909 Solutes: Electrolytes or non-electrolytes?
      • 0910 Electrolytes - strong or weak?
      • 0911 Concentrated, dilute, strong, weak
      • 0912 Species concentration vs. solution concentration
      • 0913 Weak electrolytes: Getting quantitative
    • 11 Dynamic chemical equilibrium >
      • 1100 Equilibrium: An overview
      • 1101 Visualising dynamic equilibrium
      • 1102 The jargon of equilibrium
      • 1103 Equilibrium constants
    • 22 Evidence from spectroscopy >
      • 2200 Overview, preview
      • 2201 Spectroscopy: Quantization of energies
      • 2202 Light: Wave-particle "duality"
      • 2203 UV-Visible spectroscopy
      • 2204 Beer's law
    • 27 Communicating chemistry >
      • 2700 Overview, preview
      • 2703 The jargon we use
  • TOC
  • Index
  • Teachers' area
    • T01 Communicating chemistry
    • T02 Beer's law
    • T03 Professional amnesia of the chemistry teaching professio
    • T04 Law of equilibrium
    • T05 Visusalizing dynamic chemical equilibrium
  • Aha! Whatever
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​2200   Spectroscopy:
​overview, preview

Scientists can deduce evidence about the nature of matter by analysis of the particular wavelengths of electromagnetic radiation that are absorbed by materials.

Other evidence can be deduced from the particular wavelengths of radiation that are emitted by materials when subjected to high electric potential or heating - such as the colours emitted by substances in the flames in the banner image above.
​
This field of science is called spectroscopy
.

The study of the interaction of electromagnetic radiation with matter can extend from very high-energy waves (high frequencies and short wavelengths) such as gamma rays and X-rays to very low-energy waves (low frequencies and long wavelengths) such as microwaves.

These include, but go way beyond, radiation in the visible spectrum - those wavelengths which our eyes detect as coloured light from violet to red.

Interactions of matter with different regions of the total spectrum provide evidence about different aspects of the nature of matter related to, for example, the energies of electrons, the energies of vibrations of parts of molecules, and the energies of rotation (tumbling) of molecules.

These, in turn, provide evidence about the structures of atoms and molecules.
​

Spectroscopic evidence derived from the interaction of matter with all wavelengths of radiation depend upon a phenomenon way out of our daily experience: that is, that the various forms of energy of matter are quantised. This means that energy cannot be changed continuously: it can only have certain levels (and not amounts of energy in between the "allowed" levels). What an extraordinary thing to contemplate!
​

Spectra (both emission and absorption) in the visible and ultraviolet regions of electromagnetic radiation are attributed to "transitions" between "allowed" levels of energy of electrons, while spectra in the infrared region are due to "transitions" between levels of energy of vibrations in molecules. Prof Bob gives a general explanation in Module 2201: Spectroscopy: Quantization of forms of energy.

What is light: waves, particles, or neither?

Some of the properties of radiations are consistent with them being waveforms.

However, the notion that species can absorb only particular wavelengths of radiation whose energies corresponds with the differences between levels of forms of energy is only sensible if the radiation is composed of particles (“photons”).

Light is what it is: and not a waveform and a particle, nor a waveform or a particle. Because or our inability to understand the mysterious nature of light, based on our common experiences of phenomena, scientists use a “dual nature of explanations”.

Join in a conversation with Prof Bob in Module 2202: Light: Wave-particle “duality”.
​
Using a view of light as photons, Prof Bob discusses a more detailed explanation pertaining specifically to absorption of radiations in the visible and ultraviolet in Module 2203: UV-visible spectroscopy.
​

What does the fraction of light of a particular wavelength that is absorbed (or transmitted) by a coloured solution depend on? The dependence is expressed quantitatively by Beer's law (sometimes called the Beer-Lambert law).

In Module 2204: Beer's law, Prof Bob demonstrates the basis of Beer's law through a simple activity, and shows how it can be used to analyse for the concentration of a coloured component in solution.
​

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  • Home
  • Modules
    • 02 The nature of matter >
      • 0201 Atoms: Building blocks
      • 0202 Classification of matter
    • 05 Chemical reaction, chemical equations >
      • 0500 Overview, preview
      • 0501 Amount of substance, mole
      • 0502 Avogadro constant: How many?
      • 0503 Avogadro constant: Why that number?
      • 0504 Chemical formulas: What do they mean?
      • 0505 What can equations tell us?
      • 0506 Limiting reactants
    • 09 Solutions >
      • 0901 What is a solution?
      • 0902 Miscibility of liquids
      • 0903 Like dissolves like?
      • 0905 Dissolution of ionic salts in water
      • 0906 Can we predict solubilities of salts?
      • 0907 Solution concentration
      • 0908 Chemical species, speciation
      • 0909 Solutes: Electrolytes or non-electrolytes?
      • 0910 Electrolytes - strong or weak?
      • 0911 Concentrated, dilute, strong, weak
      • 0912 Species concentration vs. solution concentration
      • 0913 Weak electrolytes: Getting quantitative
    • 11 Dynamic chemical equilibrium >
      • 1100 Equilibrium: An overview
      • 1101 Visualising dynamic equilibrium
      • 1102 The jargon of equilibrium
      • 1103 Equilibrium constants
    • 22 Evidence from spectroscopy >
      • 2200 Overview, preview
      • 2201 Spectroscopy: Quantization of energies
      • 2202 Light: Wave-particle "duality"
      • 2203 UV-Visible spectroscopy
      • 2204 Beer's law
    • 27 Communicating chemistry >
      • 2700 Overview, preview
      • 2703 The jargon we use
  • TOC
  • Index
  • Teachers' area
    • T01 Communicating chemistry
    • T02 Beer's law
    • T03 Professional amnesia of the chemistry teaching professio
    • T04 Law of equilibrium
    • T05 Visusalizing dynamic chemical equilibrium
  • Aha! Whatever
    • Playful dolphins
    • The University of Western Australia
    • Kings Park
  • Prof Bob?
    • Family
    • Travel
    • Perth
    • At work
  • Travelling
  • Contact
  • Blog
  • In four days for two days