Energy transmission in which electric and magnetic fields are propagated as waves . Visible Spectrum. Continuous spectrum. Absorption Spectra. Emission Spectra. Balmer series

1. Electromagnetic Radiation
Dr. K. Shahzad Baig
Memorial University of Newfoundland
(MUN)
Canada
Petrucci, et al. 2011. General Chemistry: Principles and Modern Applications. Pearson Canada Inc., Toronto, Ontario.
Tro, N.J. 2010. Principles of Chemistry. : a molecular approach. Pearson Education, Inc.

2. Electromagnetic Radiation
Energy transmission in which electric and magnetic fields
are propagated as waves through empty space (a vacuum)
or through a medium, such as glass.
A wave is a disturbance that transmits energy.
e.g., Water waves, sound waves, and seismic waves
In relation to the center line (the broken line),
the wave consists of crests, and troughs.

3. Amplitude,
The maximum height of the wave above the center line or the maximum depth below.
Wavelength, lambda, λ
is the distance between the tops of two successive crests (or the bottoms of two troughs),
Frequency, nu, ν,
the number of crests or troughs that
pass through a given point per unit of time.
Frequency has the unit, time-1 , s-1
The wavelength of electromagnetic radiation is shorter for high frequencies and longer
for low frequencies.

4. The visible region is only a small portion of the entire spectrum

5. An Important Characteristic of Electromagnetic Waves
The waves combine to produce the highest
crests and deepest troughs in the water. The
waves are said to be in phase.
The addition of the waves is called constructive
interference
When the waves cancel and the water is flat
And the waves are said to be out of phase.
The cancellation of the waves is called
destructive interference.
When the peak of one wave meets at the trough of another, the waves cancel each other

6. Diffraction
when a light beam (wave) encounters an obstacle, the light bends around the corners of an
obstacle or through an aperture.
Diffraction is a process by which light waves break
up into dark and light bands or into the colors of the
spectrum
Factors that impact the amount of diffraction:

7. The Visible Spectrum
The speed of light is lower in any medium than it is in a vacuum.
The speed is different in different media.
When light passes from one medium to another , it bends , called refraction of light
when a beam of white light is passed through a transparent medium, the wavelength
components are refracted differently. The light is dispersed into a band of colors,
a spectrum
When white light is passed through a glass prism
red light is refracted the least and violet light
the most
medium that disperses the sunlight is water droplets

8. Atomic Spectra
Continuous spectrum
The visible spectrum in which the diffracted light consists of many wavelength components
without gap.
Absorption Spectra
Spectra obtained by absorption of electromagnetic
radiation to the atoms, ions or molecules of sample
(UV/Visible, IR)
Emission Spectra
Spectra obtained by emission of electromagnetic
radiation to the atoms, ions or molecules of
sample (Mass)

9. Discontinuous spectrum
A spectrum between a range of wavelengths, that contains
breaks or gaps in terms of the wavelengths included.
This radiation consists of spectral lines at particular wavelengths.
This type of spectrum is a line spectrum, or atomic emission spectra
For example
Sodium burns very brightly and emits an orangish-yellow color:
Light emitted from chemical samples exhibits a discontinuous spectrum.
Low pressure Na spectrum, 350-700 nm

11. The Emission Spectra of Elements Compared with Hydrogen.
(a) hydrogen gas, which is atomized to hydrogen atoms in the discharge tube;
(b) neon; and
(c) mercury.
The strongest lines in the hydrogen spectrum are in the far UV Lyman series
starting at 124 nm and below. The strongest lines in the mercury spectrum are at
181 and 254 nm, also in the UV.
a
b
c

12. wavelength
Light from a hydrogen lamp
red light of 656.3 nm
blue line at 486.1 nm,
violet line at 434.0 nm,
violet line at 410.1 nm.
The Balmer series for hydrogen atoms

13. Quantum Theory
The energy increases from one allowed value to another.
Energy, like matter, is discontinuous. Max Plank.
The difference between any two allowed energies of a system also has a specific value,
called a quantum of energy.
Planck’s assumption was that
the group of atoms, the oscillator, must have an energy corresponding to
∈ = 𝑛ℎ𝑣 h = 6.62607 * 10-24 J s
where ϵ is the energy, n is a positive integer, ν is the oscillator frequency, and h is a constant
The energy of a quantum of electromagnetic radiation is proportional to the frequency of
the radiation. 𝐸 ∝ 𝑣

14. the hydrogen spectrum shows several series named for those who contributed most to
their determination.
the Lyman series is entirely in the UV,
the Balmer series is in the visible spectrum,
the Paschen series and others are in the IR.
Values of nf and ni are shown for some of the lines
(CC BY-SA; OpenStax)