# 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

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

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