Electromagnetic Spectrum – Properties – Instrumental Methods of Analysis B. Pharma 7th Semester

Electromagnetic Spectrum – Properties

Session Objectives

By the end of this session, students will be able to:

Ø  Explain
the properties of Electro Magnetic waves

Ø  Correlate
different components of Electro Magnetic spectrum with different Spectroscopic methods

Properties
of EM Waves

       All
matter contains charged particles that are always moving; therefore, all
objects emit EM waves.

       The
wavelengths become shorter as the temperature of the material increases.

       EM
waves carry radiant energy. 

What is the
speed of EM waves?

       All
EM waves travel 300,000 km/sec in space. (speed of light-nature’s limit!)

       EM
waves usually travel slowest in solids and fastest in gases.

Material

Speed (km/s)

Vacuum

300,000

Air

<300,000

Water

226,000

Glass

200,000

Diamond

124,000

What is the
wavelength & frequency of an EM wave?

       Wavelength=
distance from crest to crest.

       Frequency=
number of wavelengths that pass a given point in 1 s.

       As
frequency increases, wavelength becomes….

       Wavelength
(λ)= distance between
consecutive crests or troughs.

     Units: meters (m)

       Frequency
(ѵ) = number of
wavelengths that pass a given point in 1 s. The SI unit of frequency is the
hertz (Hz)/ cycles per second (cps)

       As
frequency increases, wavelength becomes smaller.

       Wave
number (ṽ) is the number of waves per unit distance 

       m-1                                             

ν=C/λ=CV

Can a wave
be a particle?

       In
1887, Heinrich Hertz discovered that shining light on a metal caused electrons
to be ejected.

       Whether
or not electrons were ejected depended upon frequency not
the amplitude of the light!  Remember
energy depends on amplitude.

       Years
later, Albert Einstein explained Hertz’s discovery:  EM waves can behave as a particle called a photon
whose energy depends on the frequency of the waves.

       Electrons
fired at two slits actually form an interference pattern similar to patterns
made by waves

What did
Young’s experiment show?

Electromagnetic
Waves

How they are formed

Waves made by vibrating electric charges that can travel
through space where there is no matter

Kind of wave

Transverse with alternating electric and magnetic fields

Sometimes behave as

Waves or as Particles (photons)

EMR and
Spectroscopy

Technique

Type of Electromagnetic Radiation

Type of Matter Observed

Type of Interaction

Ultraviolet-Visible Spectroscopy
(UV-Vis Spectroscopy)

Ultraviolet and
Visible radiation

Electrons and
electronic excitations

Absorbance

Infrared Spectroscopy
(IR Spectroscopy)

Infrared radiation

Molecular
rotations, molecular vibrations, bonds between atoms

Absorbance (or
transmittance)

Fluorescence Spectroscopy

Ultraviolet and
Visible radiation

Electrons and
electronic excitations

Emission

Nuclear Magnetic Resonance Spectroscopy (NMR
Spectroscopy)

Radiowaves

Nucleus

Resonance or
Coherance

Flame emission spectroscopy (Flame photometry)

Ultraviolet and
Visible radiation

Atoms

Emission

X-Ray Diffraction Crystallography

X-rays

Electron
denisities

Diffraction or
Scattering

Atomic Absorption and Emission Spectroscopy

Ultraviolet and
Visible radiation

Atoms

Absorption or
Emission

ESR Spectroscopy

Microwaves

Free radicals

Absorption

Certain
terms used in spectroscopy

       Spectroscopy

       Spectrophotometry

       Spectrometer:
an instrument with an entrance
slit, a dispersing device, and one or more exit slits, with which measurements
are made at selected wavelengths within the spectral range, or by scanning over
the range. The quantity detected is a function of radiant power

       Photometer
an instrument used in
photometry, usually one that compares the illumination produced by a particular
light source with that produced by a standard source 

       Spectrophotometer:
A spectrophotometer is a
combination of two instruments, namely a spectrometer for producing
light of any selected color (wavelength), and a photometer for measuring
the intensity of light.

SUMMARY

       Wavelength=
distance from crest to crest.

       Frequency=
number of wavelengths that pass a given point in 1 s.

       Wave
number (ṽ) is the number of waves per unit distance 

       m-1                                            

      

ν=C/λ=CV

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