X-ray diffraction from the crystal of a protein (hen egg lysozyme) produced this interference pattern. Analysis of the pattern yields information about the structure of the protein. (credit: “Del45”/Wikimedia Commons)
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.
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 (
) 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.
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 (
) 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.
What is the minimum frequency of a photon required to ionize: (a) a
ion in its ground state? (b) A
ion in its first excited state?
For
, one electron “orbits” a nucleus with two protons and two neutrons (
). 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
ion to infinity is negative the value of the ground state energy, written:
Thus, the energy to ionize the electron is
Similarly, the energy needed to remove an electron in the first excited state of
ion to infinity is negative the value of the first excited state energy, written:
the study of living organisms and their interactions with one another and their environment.
Wine
discuss the biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles in an essay form
advantage of electronic microscope is easily and clearly while disadvantage is dangerous because its electronic. advantage of light microscope is savely and naturally by sun while disadvantage is not easily,means its not sharp and not clear
Abdullahi
cell theory state that every organisms composed of one or more cell,cell is the basic unit of life
Abdullahi
is like gone fail us
DENG
cells is the basic structure and functions of all living things
A scanning electron microscope (SEM) is ideal for situations requiring high-resolution imaging of surfaces. It is commonly used in materials science, biology, and geology to examine the topography and composition of samples at a nanoscale level. SEM is particularly useful for studying fine details,
