atomic spectra

Examples of atomic spectra in the following topics:

• Hydrogen Spectra

  • For decades, many questions had been asked about atomic characteristics.
  • From their sizes to their spectra, much was known about atoms, but little had been explained in terms of the laws of physics.
  • (It was a running joke that any theory of atomic and molecular spectra could be destroyed by throwing a book of data at it, so complex were the spectra.)
  • In some cases, it had been possible to devise formulas that described the emission spectra.
  • As you might expect, the simplest atom—hydrogen, with its single electron—has a relatively simple spectrum.

• Nuclear Size and Density

  • It can be measured by the scattering of electrons by the nucleus and also inferred from the effects of finite nuclear size on electron energy levels as measured in atomic spectra.
  • The problem of defining a radius for the atomic nucleus is similar to the problem of atomic radius, in that neither atoms nor their nuclei have definite boundaries.
  • Nuclear density is the density of the nucleus of an atom, averaging about $4 \cdot 10^{17} \text{kg/}\text{m}^3$.
  • Top: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed.Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge.

• Energy of a Bohr Orbit

  • To be more general, we note that this analysis is valid for any single-electron atom.
  • So, if a nucleus has $Z$ protons ($Z=1$ for hydrogen, $Z=2$ for helium, etc.) and only one electron, that atom is called a hydrogen-like atom.
  • The spectra of hydrogen-like ions are similar to hydrogen, but shifted to higher energy by the greater attractive force between the electron and nucleus.
  • This is consistent with the planetary model of the atom.
  • The energy of the $n$-th level for any atom is determined by the radius and quantum number:

• The Bohr Model of the Atom

  • In 1913, after returning to Copenhagen, he began publishing his theory of the simplest atom, hydrogen, based on the planetary model of the atom.
  • From their sizes to their spectra, much was known about atoms, but little had been explained in terms of the laws of physics.
  • This atom model is disastrous, because it predicts that all atoms are unstable.
  • Therefore, his atomic model is called a semiclassical model.
  • Niels Bohr, Danish physicist, used the planetary model of the atom to explain the atomic spectrum and size of the hydrogen atom.

• X-Ray Spectra: Origins, Diffraction by Crystals, and Importance

  • X-ray shows its wave nature when radiated upon atomic/molecular structures and can be used to study them.
  • However, since atoms and atomic structures have a typical size on the order of 0.1 nm, x-ray shows its wave nature with them.
  • When x-ray are incident on an atom, they make the electronic cloud move as an electromagnetic wave.
  • This is called Rayleigh Scattering, which you should remember from a previous atom.
  • Not only do x-rays confirm the size and shape of atoms, they also give information on the atomic arrangements in materials.

• Beta Decay

  • Beta decay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted from an atomic nucleus.
  • Beta decay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted from an atomic nucleus, as shown in .
  • Beta decay is a process that allows the atom to obtain the optimal ratio of protons and neutrons.
  • The continuous energy spectra of beta particles occur because Q is shared between a beta particle and a neutrino.
  • β decay in an atomic nucleus (the accompanying antineutrino is omitted).

• Matter and Antimatter

  • For example, a positron (the antiparticle of the electron, with symbol e+) and an antiproton (symbol p-) can form an antihydrogen atom .
  • Antimatter galaxies, if they exist, are expected to have the same chemistry and absorption and emission spectra as normal-matter galaxies, and their astronomical objects would be observationally identical, making them difficult to distinguish from normal-matter galaxies.

• X-Rays

  • When the electrons hit the target, x-rays are created through two different atomic processes:
  • X-ray fluorescence, if the electron has enough energy that it can knock an orbital electron out of the inner electron shell of a metal atom.
  • Its unique features are x-ray outputs many orders of magnitude greater than those of x-ray tubes, wide x-ray spectra, excellent collimation, and linear polarization.

• The Michelson Interferometer

  • As shown in previous atoms, when two waves with the same frequency combine, the resulting pattern is determined by the phase difference between the two.
  • It has played an important role in studies of the upper atmosphere, revealing temperatures and winds (employing both space-borne and ground-based instruments) by measuring the Doppler widths and shifts in the spectra of airglow and aurora.

• Spectra