Why don’t atoms emit a continuous spectrum?

Question

Hello. I have 2 questions regarding Astronomy.

1. Why don’t atoms emit a continuous spectrum?

&

2. How can you tell what sort of gas is emitting light?

Thank you for your help! <3

Answer 1

Why don’t atoms emit a continuous spectrum? Because they don't work that way. Atoms emit photons when electrons jump from a higher energy level to a lower one; the difference in energy between the two levels is emitted as a photon. Since energy levels are fixed, a jumping electron can only emit a precise amount of energy, which means a photon with a precise wavelength/frequency.

How can you tell what sort of gas is emitting light? Well, each element has its own spectral signature. So you look at the spectrum, isolate all element signatures, and start thinking about what compound might contain all those elements...

Answer 2

Atoms can and do emit continuous spectra. Ionized atoms which capture an electron will emit a continuous spectrum. Atoms in high pressure gas, liquid and solid phases will emit continuous spectra. If you want an atom to emit a line spectrum, you have to isolate it from other atoms and make sure that you only excite transitions of its electron between their bound states.

Therefor, strictly speaking, your first question only has an answer under specific conditions. Once you have your atoms under these conditions, you can tell them apart by the frequency/wavelength of the light they are emitting because no two elements have exactly the same electronic configuration.

More importantly, by looking at the line width and the continuous part of the spectra atoms and molecules are emitting, scientists can tell something about the conditions they are in, like local temperature and density. This is as important as the identification of elements itself.

Answer 3

This should point you in the right direction:
1) Because energy is quantized (think electron orbitals and how light is emitted in the first place).
2) Each element has a unique spectral signature (look up ionization energies and so forth).