Question

Atomic spectrum is an example of

• A. Line spectra
• B. Continuous spectra
• C. Line and continuous spectra-both
• D. Band spectra

Hint:

Remember:
Atoms (isolated) $\rightarrow$ Line Spectra (sharp electronic transitions).
Molecules $\rightarrow$ Band Spectra (electronic, vibrational, and rotational transitions).
Hot dense solids (Bulbs) $\rightarrow$ Continuous Spectra.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
When atoms absorb or emit electromagnetic radiation (light), the resulting spectrum is studied to understand their electronic structures.
According to quantum mechanics and Bohr's atomic model, electrons inside an atom can only occupy discrete, quantized energy levels (\( E_1, E_2... \)).
Transitions of electrons between these quantized energy levels involve the absorption or emission of photons with highly specific, discrete energies:
\[ \Delta E = h\nu = \frac{hc}{\lambda} \]
Where:
\( \Delta E \) is the energy difference between the two states.
\( \lambda \) is the specific wavelength of light absorbed or emitted.

Step 2: Detailed Explanation:
Because the energy levels in an isolated gaseous atom are strictly quantized, the light emitted or absorbed consists only of specific, discrete wavelengths.
When this light is passed through a spectroscope, it appears as a series of sharp, narrow, colored lines against a dark background (emission spectrum) or dark lines against a bright background (absorption spectrum).
Therefore, the atomic spectrum is a classic example of a Line Spectrum (Option A).
Let us compare this with the other types of spectra:
1. Continuous Spectra:
A continuous spectrum contains all wavelengths of light within a given range without any gaps, displaying a continuous blend of colors (like a rainbow).
This is produced by hot, dense solids, liquids, or highly compressed gases (such as the incandescent filament of a bulb or blackbody radiation from stars).
2. Band Spectra:
A band spectrum consists of groups of closely spaced lines that appear as continuous bands separated by dark spaces.
This is characteristic of molecules (molecular spectra), where the transitions involve closely spaced vibrational and rotational energy levels in addition to electronic transitions.
Atomic spectra do not display continuous or band-like behavior under standard conditions because they originate from isolated, non-interacting atoms.

Step 3: Final Answer:
Thus, the atomic spectrum is characterized as a Line spectrum.