Chemistry · Structure Of Atom · NEET
In an emission spectrum, an excited atom releases energy and you see bright coloured lines on a dark background. In an absorption spectrum, white light is passed through the atoms and they absorb certain wavelengths, so you see dark lines on a bright continuous background. NCERT calls the absorption spectrum the 'photographic negative' of the emission spectrum. Very important point for NEET: the dark lines in absorption appear at the SAME wavelengths as the bright lines in emission, because the same energy jumps are involved.
Because the energy of an electron in an atom is quantized. The electron can only sit in fixed energy levels, so when it jumps, it can only emit or absorb certain fixed amounts of energy (fixed wavelengths). This gives separate bright lines with dark gaps between them. White light, on the other hand, contains all wavelengths, so passing it through a prism gives a continuous spectrum (a full rainbow with no gaps). This is why line spectra are also called 'atomic spectra'.
A continuous spectrum has every wavelength from violet to red with no gaps, like sunlight or white light spread by a prism. A line spectrum has only a few specific bright wavelengths (lines) with dark spaces in between. Simple rule: continuous = full rainbow, line = a few separate lines. Hot glowing solids or filaments give continuous spectra; excited gaseous atoms give line spectra.
Yes. For the same element, the wavelengths absorbed are exactly the wavelengths it can emit. So the dark lines in the absorption spectrum line up perfectly with the bright lines in the emission spectrum. This is why NCERT says one is the negative of the other. NEET often tests this idea directly.
Because every element has its OWN unique set of spectral lines. No two elements give the same pattern. So scientists can identify an unknown element just by matching its lines, exactly like matching fingerprints. NCERT mentions elements like Rb, Cs, Ga and even helium (found in the Sun) were discovered this way using spectroscopy.
When the electron jumps to a HIGHER level (nf greater than ni), energy is absorbed, this gives an absorption line. When the electron falls to a LOWER level (ni greater than nf), energy is released as light, this gives an emission line. Same wavelength either way, only the direction of the jump changes. For hydrogen, the Balmer series (jumps ending at n=2) gives the visible lines.
Which of the following series of transitions in the spectrum of the hydrogen atom falls in the visible region?
The ratio of the wavelengths of the light absorbed by a hydrogen atom when it undergoes n=2 to n=3 and n=4 to n=6 transitions, respectively, is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Emission spectrum = BRIGHT coloured lines on a DARK background. The atom gives out light. Absorption spectrum is the reverse: dark lines on a bright continuous background.
They mean the same thing. NCERT says atomic emission spectra are line spectra, so 'line spectrum' and 'atomic spectrum' are used interchangeably for the bright-line spectra of gaseous atoms.
In a hot solid the atoms are packed close and their energy levels blur together, giving all wavelengths (continuous). In a gas the atoms are far apart with sharp, separate energy levels, so only fixed wavelengths appear (line spectrum).
The visible region. Balmer lines come from electrons falling to n=2 and are the only hydrogen lines you can see with the eye. This is a very common NEET question.
Spectroscopy is the study of emission or absorption spectra. It is used to identify unknown elements by matching their spectral lines, and it was how elements like caesium, rubidium and even helium were discovered.
