Chemistry class 12th Atomic spectra

Atomic Spectra: Full Explanation


1. Introduction to Atomic Spectra
Atomic spectra are the unique patterns of light emitted or absorbed by atoms when electrons
transition between energy levels. These spectra provide crucial insights into atomic structure and
are widely used in spectroscopy, astrophysics, and quantum mechanics.

2. Types of Atomic Spectra
(a) Emission Spectrum
- Produced when an atom's electrons fall from a higher energy level to a lower energy level, emitting
energy as light.
- The emitted light appears as bright lines on a dark background.
- Example: The hydrogen emission spectrum (Balmer series, Lyman series, etc.).


(b) Absorption Spectrum
- Occurs when an atom absorbs energy, causing electrons to jump to higher energy levels.
- The spectrum appears as dark lines on a continuous spectrum, as specific wavelengths are
absorbed.
- Example: The Sun's spectrum contains absorption lines known as Fraunhofer lines.


(c) Continuous Spectrum
- Produced by a hot, dense object (like a star or a filament bulb).
- Contains all wavelengths without any gaps or lines.

3. Explanation Using Bohr's Model
Bohr's atomic model explains atomic spectra in terms of electron transitions:
- Electrons in an atom exist in quantized energy levels (n=1, 2, 3, ...).
- When an electron absorbs energy, it moves to a higher energy level (excited state).
- When it returns to a lower energy level (ground state), it emits energy in the form of light (photons).


The energy of emitted or absorbed light is given by:


DeltaE = E_2 - E_1 = h f


where:
- h = Planck's constant (6.626 × 10^-34 J·s)
- f = Frequency of emitted or absorbed radiation