Spectroscopy , atomic spectrum and types with explanations,examples,and graphs

1. SPECTROSCOPY & ATOMIC
SPECTRUM
BY : SAIRA KANWAL AWAN

3. What is spectroscopy?
• Branch of physics deals with the study of interaction between matter
and electromagnetic radiation.
• It is originated through the study of visible light dispersed by prism.

4. HISTORY
• In 1814 JOSEPH FRAUENHOFER an optician in MUNICH ,
discovered many dark lines crossing the spectrum of sun.
• In 1814 Fraunhofer invented the spectrum.
• It used to measure the properties of light.
• It works by breaking light into different wavelengths.These are made
of prisms as light passes through glass , different wavelengths slow
down by different amounts and are burnt into their colours.

5. SPECTRUM & SPECTROMETER
• Spectrometer: An instrument used to measure the wavelengths of
light.
• Spectrum: A plot of the colour profile (wavelengths present).

6. TYPES OF SPECTROSCOPY
• There are three type of spectrum:
• Continuous spectrum.
• Band spectrum or emission spectrum.
• Discrete/line spectrum or absorption spectrum.

7. CONTINUOUS SPECTRUM
• A spectrum ( as of light emitted by white – hot lamp filament ) having
no apparent breaks or gaps throughout its wavelength range.
• Consists of continum wavelengths.

8. BAND OR EMISSION SPECTRUM
• These are produced by molecules radiating their rotational or
vibrational energies, or both simultaneously.
• When number of atoms is large one gets continuum of energy levels ,
so called “spectral bands”.

9. DISCRETE SPECTRUM
• A physical quantity is said to have a discrete spectrum if it takes only
distinct values and the next.
• Seen in emission and absorption spectrum of isolated atoms of a
chemical element, which only absorbs and emit light at particular
wavelength.

10. ATOMIC SPECTRUM
• Atomic spectrum is an effect of quantized orbiys of electrons around
the atom.
• The range of characteristic frequencies of electromagnetic radiation
that are readily absorbed and emitted by an atom.
• When electron excites e.g. By heating , additional energy pushes
electron to higher energy levels.
• When electron fall back down in the form of photon. These emitted
photons form the elements spectrum colours.
• Newton identified these 7 colours (red, orange , yellow , green , blue
, indigo , violet).

11. ATOMIC HYDROGEN SPECTRUM
• The emission spectrum of atomic hydrogen has
been divided into number of spectural series.
• Wavelengths are given by RYDBERG FORMULA.
• These observed spectral lines are due to the
electron making transition between two energy
levels is atom.
• Hydrogen emit red light because of its 4 characteristic lines most
intense line is red at 656 nm.

12. REGULARITIES IN HYDROGEN SPECTRUM
• Spectral lines lie in three regions Visible region , Ultraviolet region ,
Infrared region.
• Ultraviolet consists of Lyman series.
• Visible region consists of Balmer series.
• Infrared region consists of Pashen series , Bracket series , Pfund
series.
• The spacing of spectral lines decreaaes as we go towards
wavelengths.
• The wavelengths (colours) themselves approach a limit called Series
limit.

13. LYMAN SERIES
• Spectral lines for Lyman series is transition from n > 2 to n= 1 , which
lies in the UV region.
• Longest wavelength corresponding m = 2 is 121.57 nm.
• Shorter wavelength is m = infinity is 91.18 nm.
• These wavelengths are the reasons for Lyman series to fall on UV
region.

14. BALMER SERIES
• In 1885 , Balmer developed an empirical formula for wavelengths of
spectral lines of hydrogen spectrum.

15. PASCHEN SERIES