Emission spectra?

Question

Why, when atoms of elements are heated, do they give off light, even though sometimes this light is not visible?

I think I understand the basics. When an atom is heated, an electron can become unstable, jumping to a higher energy level where it is unstable. It returns to its lower energy level, releasing energy in the form of light.
However, I'd like to answer the question in more detail and with more understanding. How do you get white light? And why, when the light is passed through a spectroscope, does the image consist of seperate coloured lines?
And how can we identify an element by its emission spectra?
If you could help I'd be very grateful.

Answer 1

First of all congrats for your correct understanding. Let us now see the points raised, one by one.

White light is light of all colors. So we see it as white light. Absence of color gives white light.

When you pass the white light through a spectroscope which consists of a prism or a grating, the difffraction of different wavelengths of light gives rise to intensity peaks at different frequencies and we perceive the different frequencies as different colors.

Emission spectra consist of continuous and characteristic spectral lines. When the electron falls from a higher orbit to a lower orbit, a well defined light of a definite wavelength (and thus frequency ) is emitted. for other excitation and emissio, the frequencies are not defined. By looking at the characteristic spectral lines (which are characteristic of a given element), we can identify the presence of a given element and can approximately tell the relative concentration of that element. Quantitative analysis is done by calibrating the photmultiplier tubes which are used as detectors. You will find more information from text-books, articles and manufacturer's literature.

Answer 2

You are right that electrons transferring to and from different energy levels either absorb or release photons of certain energies and frequencies.

When you have an amount of a substance, you have literally billions of atoms (not just one), each having electrons going through different transitions at different times. That is why certain materials have differing line spectra due to the 'allowed energy levels' within that specific atom.

Hydrogen has completely different allowed energy levels to helium and so on.

The allowed energy levels are governed by the allowed Quantum numbers for the particular atoms, regarding the magnetic moment and spin of particular electron orbits. The electrons must have discreet energy levels i.e. they can only be of a certain value - the energy range is not continuous.

Say for hydrogen-:
n=1 -13.6eV
n=2 - 3.4 eV
n=3 - 1.5 eV

A transition from n=3 to n=2 releases a specific amount of energy, in this case -1.8 eV, which then corresponds to a certain photon frequency which will be released. A transition from n=3 to n=1 (- 12.1 eV) would be a completely different photon emission, thus the different line spectra are produced.

Remember only the Balmer Series of transitions emits photons in the visible range for humans, most other series emit in the Infra-Red (Paschen Series) or Ultra Violet (Lyman Series) range.

Hope this helps.

Answer 3

emission spectrum - is the spectrum of frequencies of electromagnetic radiation emitted as a results of an atom's electrons making a transition from a excessive power state to a decrease power state. The power of the emitted photon is comparable to the ability distinction between the two states. abortion spectrum i dont understand . sorry