This document discusses spectroscopy and atomic spectra. Spectroscopy is the study of interaction between matter and electromagnetic radiation. There are three main types of atomic spectra: continuous spectra which have no gaps in wavelengths, band or emission spectra produced by molecules radiating energy in rotational or vibrational transitions, and discrete line spectra seen in isolated atom absorption and emission at particular wavelengths. Atomic spectra result from electrons transitioning between quantized energy levels of an atom when excited, and hydrogen emits characteristic wavelengths that form different spectral series depending on the electron transition.

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