how can elements with low atomic numbers have many spectral lines?

Answer 1

Spectral lines are formed when electrons make transitions between THEIR own energy levels. The atomic numbers themselves determine the scales of those energy levels, and the greater the charge the more complicated the distribution of them is, in general.

However, even for hydrogen (atomic number 1), there is an extremely large number of energy levels. In an otherwise empty universe, there would be an infinite number; however, even in almost empty space the presence of other material, although extremely diffuse, affects the highermost levels, rendering them not individually accessible --- the other particles won't let electrons occupy those highest levels undisturbed. Those levels effectively cease to exist under such conditions. (We say that "the continuum [of free states] has been lowered.")

The principal energy levels of hydrogen are of the form

- Ry (1/n^2) for n = 1, 2, 3, ... etc. [Ry is the "Rydberg constant."]

Many SERIES of lines exist, corresponding to the following energy differences. The series are named in the order following that:

E_nm = Ry (1/n^2 - 1/m^2),for m = (n +1), (n+2), (n + 3), ...

The series' names are:

Lyman (n = 1), Balmer (2), Paschen (3), Brackett (4), Pfund (5)... . The familiar optical spectrum of hydrogen (also known as H alpha, H beta, etc.) is the Balmer series.

With Bohr's work in 1912, the Rydberg constant became known in terms of more fundamental quantities. It is proportional to Z^2, where Z is the atomic charge of the nuclei. As such, it applies to all hydrogen-like (called "hydrogenic") atoms, that is to atoms with all but one electron ionized. Thus He II (Z = 2, one electron left) has corresponding energy levels four times deeper than those of neutral hydrogen. Therefore many of its lines essentially correspond with some of hydrogen's lines. [I say "essentially" rather than "exactly equal," because careful analysis, allowing for the influence of the different masses of the nuclei, changes the energy levels and therefore the spectral lines' wavelengths, by terms of order (electron mass) / (nucleus mass), or roughly speaking 1 part in 1840 or less. Loosely speaking, shifts of the order of an angstrom or two are therefore possible.]

Live long and prosper.

Answer 2

melissa,

i think (i have no source) but i think that if it gains electrons you may be able to get more spectral lines - like nitrogen. so if you want a gas to have 'many spectral lines' you could make sure it has its shells full. other than attracting other atoms to fill the empty shells would it make sence to static charge the gas?

i am a little of a newbie at this but this is a little borderline on my knowledge - sorry if i cannot help more.

Maussy,
you said "These excited shells are not stable and the electron release a photon with energy "

Under what circumstances could they be stable?

also regarding a Hydrogen Spectrum tube it creates Red (656.3) , blue (486.1nm), UV? (434.0nm and 410.2nm)
can i just energise it enough so that i get the first 2 - probably could...

the source also says that it emits Infra red but from what i have seen so far (on lists of emmited light of other sources) it is visible red so the page may be wrong.

If you can help me understand - thank you!

Answer 3

the spectral lines are due to electrons of an atom leaping from 1 energy level to another. It is not proportional to the number of electrons in the atom.
When you excite an electron it does not stay in its lowest state it jumps to a level to accommodate the extra energy. When it jumps back down it emits this energy as light of a particular frequency.
If you have a tube of hydrogen (for example) the jumps that the electron of each atom makes is only determined by the energy it has absorbed. Different hydrogen atoms will have absorbed different amounts of energy so emit different frequencies.

Answer 4

You have a spectral line when an electron jumps from an outer shell to a more inner shell.
Suppose we have hydrogen : In the . If fundamental state ,the single electron is on shell K n=1 . if you give enough energy the electron can be excited and jump to an upper shell l, m ,n ,o
These excited shells are not stable and the electron release a photon with energy = El -Ek , Em -Ek En -Ek , this give a line with different but well definite energies.