+ 79 is the maximum number of electrons in the first energy shell of an atom.
what is the maximum number of electrons in the first energy shell of an atom?
+ 79
lewis proposed that an atom forms enough covalent bonds to form a full (or closed) outer electron shell. in the diagram of methane shown here, the carbon atom has a valence of four and is, therefore, surrounded by eight electrons (the octet rule), four from the carbon itself and four from the hydrogens bonded to it. each hydrogen has a valence of one and is surrounded by two electrons (a duet rule) – its own one electron plus one from the carbon. the numbers of electrons correspond to full shells in the quantum theory of the atom; the outer shell of a carbon atom is the "n" = 2 shell, which can hold eight electrons, whereas the outer (and only) shell of a hydrogen atom is the "n" = 1 shell, which can hold only two.
covalent bond
to stimulate the emission of characteristic x-rays from a specimen, a high-energy beam of charged particles such as electrons or protons (see pixe), or a beam of x-rays, is focused into the sample being studied. at rest, an atom within the sample contains ground state (or unexcited) electrons in discrete energy levels or electron shells bound to the nucleus. the incident beam may excite an electron in an inner shell, ejecting it from the shell while creating an electron hole where the electron was. an electron from an outer, higher-energy shell then fills the hole, and the difference in energy between the higher-energy shell and the lower energy shell may be released in the form of an x-ray. the number and energy of the x-rays emitted from a specimen can be measured by an energy-dispersive spectrometer. as the energies of the x-rays are characteristic of the difference in energy between the two shells and of the atomic structure of the emitting element, eds allows the elemental composition of the specimen to be measured.
energy-dispersive x-ray spectroscopy