# 8.5 Atomic spectra and x-rays  (Page 6/12)

 Page 6 / 12

## Summary

• Radiation is absorbed and emitted by atomic energy-level transitions.
• Quantum numbers can be used to estimate the energy, frequency, and wavelength of photons produced by atomic transitions.
• Atomic fluorescence occurs when an electron in an atom is excited several steps above the ground state by the absorption of a high-energy ultraviolet (UV) photon.
• X-ray photons are produced when a vacancy in an inner shell of an atom is filled by an electron from the outer shell of the atom.
• The frequency of X-ray radiation is related to the atomic number Z of an atom.

## Conceptual questions

Atomic and molecular spectra are discrete. What does discrete mean, and how are discrete spectra related to the quantization of energy and electron orbits in atoms and molecules?

Atomic and molecular spectra are said to be “discrete,” because only certain spectral lines are observed. In contrast, spectra from a white light source (consisting of many photon frequencies) are continuous because a continuous “rainbow” of colors is observed.

Discuss the process of the absorption of light by matter in terms of the atomic structure of the absorbing medium.

NGC1763 is an emission nebula in the Large Magellanic Cloud just outside our Milky Way Galaxy. Ultraviolet light from hot stars ionize the hydrogen atoms in the nebula. As protons and electrons recombine, light in the visible range is emitted. Compare the energies of the photons involved in these two transitions.

UV light consists of relatively high frequency (short wavelength) photons. So the energy of the absorbed photon and the energy transition ( $\text{Δ}E$ ) in the atom is relatively large. In comparison, visible light consists of relatively lower-frequency photons. Therefore, the energy transition in the atom and the energy of the emitted photon is relatively small.

Why are X-rays emitted only for electron transitions to inner shells? What type of photon is emitted for transitions between outer shells?

How do the allowed orbits for electrons in atoms differ from the allowed orbits for planets around the sun?

For macroscopic systems, the quantum numbers are very large, so the energy difference ( $\text{Δ}E$ ) between adjacent energy levels (orbits) is very small. The energy released in transitions between these closely space energy levels is much too small to be detected.

## Problems

What is the minimum frequency of a photon required to ionize: (a) a ${\text{He}}^{+}$ ion in its ground state? (b) A ${\text{Li}}^{\text{2+}}$ ion in its first excited state?

For ${\text{He}}^{+}$ , one electron “orbits” a nucleus with two protons and two neutrons ( $Z=2$ ). Ionization energy refers to the energy required to remove the electron from the atom. The energy needed to remove the electron in the ground state of ${\text{He}}^{+}$ ion to infinity is negative the value of the ground state energy, written:
$E=-54.4\phantom{\rule{0.2em}{0ex}}\text{eV}.$
Thus, the energy to ionize the electron is $\text{+54.4}\phantom{\rule{0.2em}{0ex}}\text{eV.}$
Similarly, the energy needed to remove an electron in the first excited state of ${\text{Li}}^{\text{2+}}$ ion to infinity is negative the value of the first excited state energy, written:
$E=-30.6\phantom{\rule{0.2em}{0ex}}\text{eV}.$
The energy to ionize the electron is 30.6 eV.

how does colour appear in thin films
in the wave equation y=Asin(kx-wt+¢) what does k and w stand for.
derivation of lateral shieft
Hi
Hi
hi
ALFRED
how are you?
hi
asif
hi
Imran
I'm fine
ALFRED
total binding energy of ionic crystal at equilibrium is
How does, ray of light coming form focus, behaves in concave mirror after refraction?
Sushant
What is motion
Anything which changes itself with respect to time or surrounding
Sushant
good
Chemist
and what's time? is time everywhere same
Chemist
No
Sushant
how can u say that
Chemist
do u know about black hole
Chemist
Not so more
Sushant
DHEERAJ
Sushant
But ask anything changes itself with respect to time or surrounding A Not any harmful radiation
DHEERAJ
explain cavendish experiment to determine the value of gravitational concept.
For the question about the scuba instructor's head above the pool, how did you arrive at this answer? What is the process?
as a free falling object increases speed what is happening to the acceleration
of course g is constant
Alwielland
acceleration also inc
Usman
which paper will be subjective and which one objective
jay
normal distributiin of errors report
Dennis
normal distribution of errors
Dennis
photo electrons doesn't emmit when electrons are free to move on surface of metal why?
What would be the minimum work function of a metal have to be for visible light(400-700)nm to ejected photoelectrons?
give any fix value to wave length
Rafi
40 cm into change mm
40cm=40.0×10^-2m =400.0×10^-3m =400mm. that cap(^) I have used above is to the power.
Prema
i.e. 10to the power -2 in the first line and 10 to the power -3 in the the second line.
Prema
there is mistake in my first msg correction is 40cm=40.0×10^-2m =400.0×10^-3m =400mm. sorry for the mistake friends.
Prema
40cm=40.0×10^-2m =400.0×10^-3m =400mm.
Prema
this msg is out of mistake. sorry friends​.
Prema
what is physics?
why we have physics
because is the study of mater and natural world
John
because physics is nature. it explains the laws of nature. some laws already discovered. some laws yet to be discovered.
Yoblaze
physics is the study of non living things if we added it with biology it becomes biophysics and bio is the study of living things tell me please what is this?
tahreem
physics is the study of matter,energy and their interactions
Buvanes
all living things are matter
Buvanes
why rolling friction is less than sliding friction
tahreem
thanks buvanas
tahreem
is this a physics forum