core electrons

Examples of core electrons in the following topics:

• The Shielding Effect and Effective Nuclear Charge

  • The attraction between this lone valence electron and the nucleus with 11 protons is shielded by the other 10 core electrons.
  • Ne has 10 electrons.
  • Thus the number of nonvalence electrons is 2 (10 total electrons - 8 valence).
  • Flourine has 9 electrons but F- has gained an electron and thus has 10.
  • Sodium has 11 electrons but the Na+ ion has lost an electron and thus has 10.

• Electromagnetic Spectrum

  • Photon energy is directly proportional to the wave frequency, so gamma ray photons have the highest energy (around a billion electron volts), while radio wave photons have very low energy (around a femto-electron volt).
  • An example would be the oscillation of the electrons in an antenna.
  • Ultraviolet: Excitation of molecular and atomic valence electrons, including ejection of the electrons (photoelectric effect).
  • X-rays: Excitation and ejection of core atomic electrons, Compton scattering (for low atomic numbers).
  • Gamma rays: Energetic ejection of core electrons in heavy elements, Compton scattering (for all atomic numbers), excitation of atomic nuclei, including dissociation of nuclei.

• Electron Configurations of Atoms

  • Electron shell #1 has the lowest energy and its s-orbital is the first to be filled.
  • In the third period of the table, the atoms all have a neon-like core of 10 electrons, and shell #3 is occupied progressively with eight electrons, starting with the 3s-orbital.
  • The highest occupied electron shell is called the valence shell, and the electrons occupying this shell are called valence electrons.
  • The chemical properties of the elements reflect their electron configurations.
  • These atoms have only one electron in the valence shell, and on losing this electron arrive at the lower shell valence octet.

• Electronegativity and Oxidation Number

  • Electronegativity is a property that describes the tendency of an atom to attract electrons (or electron density) toward itself.
  • The higher its electronegativity, the more an element attracts electrons.
  • Properties of a free atom include ionization energy and electron affinity.
  • Where electrons are in space is a contributing factor because the more electrons an atom has, the farther from the nucleus the valence electrons will be, and as a result they will experience less positive charge; this is due to their increased distance from the nucleus, and because the other electrons in the lower-energy core orbitals will act to shield the valence electrons from the positively charged nucleus.
  • One way to characterize atoms in a molecule and keep track of electrons is by assigning oxidation numbers.

• Reactions of Aromatic Compounds

  • The electrons in the pi system of the benzene ring are responsible for the reactivity observed.
  • While aromatic compounds are best represented by a continuous electron density evenly distributed around the aromatic core, the alternating single and double bonds that are commonly drawn are very useful when predicting the reactivity of aromatic compounds.
  • The presence of an electron-withdrawing group on the ring can speed up the progress of this class of reactions.
  • It states that an electron-donating substituent generally accelerates substitution and directs reactivity toward the positions that are ortho and para to it on the ring, while an electron-withdrawing substituent will slow reaction progress and favor the meta position on the ring.
  • Due to the electrons provided by the NH2 group, this intermediate is stabilized, and the para-substitution is favored.

• Aluminum

  • Trivalent aluminum is electron-deficient and therefore exceptionally useful as a Lewis acid, particularly in organic synthesis.
  • Outer shells of consumer electronics, also cases for equipment (e.g. photographic equipment)
  • Substrate material of metal-core copper clad laminates used in high brightness LED lighting

• Coloring Agents

  • Many of the properties of metal complexes are dictated by their electronic structures.
  • This approach is the essence of crystal field theory (CFT), which is a core concept in inorganic chemistry.
  • However, the electron remains centered on the metal.
  • The overall charge of the system remains the same, but the localization of the electron changes.
  • These phenomena can be observed with the aid of electronic spectroscopy (also known as UV-Vis).

• Benzene and other Aromatic Compounds

  • As experimental evidence for a wide assortment of compounds was acquired, those incorporating this exceptionally stable six-carbon core came to be called "aromatic".
  • This further confirms the previous indication that the six-carbon benzene core is unusually stable to chemical modification.
  • Here, two structurally and energetically equivalent electronic structures for a stable compound are written, but no single structure provides an accurate or even an adequate representation of the true molecule.
  • An alternative representation for benzene (circle within a hexagon) emphasizes the pi-electron delocalization in this molecule, and has the advantage of being a single diagram.
  • The remaining carbon valence electrons then occupy these molecular orbitals in pairs, resulting in a fully occupied (6 electrons) set of bonding molecular orbitals.

• Electronic Effects

  • Such charges are produced by removing (or adding) electrons from (or to) an object.
  • Electron deficient species, which may or may not be positively charged, are attracted to electron rich species, which may or may not be negatively charged.
  • Electrophiles: Electron deficient atoms, molecules or ions that seek electron rich reaction partners.
  • Nucleophiles: Electron rich atoms, molecules or ions that seek electron deficient reaction partners.

• General Rules for Assigning Electrons to Atomic Orbitals

  • An atom's electrons exist in discrete atomic orbitals, and the atom's electron configuration can be determined using a set of guidelines.
  • This nucleus is surrounded by electrons.
  • An atom's electron shell can accommodate 2n2 electrons, where n is the energy level.
  • An element's electron configuration is the arrangement of the electrons in the shells.
  • Electrons that occur together in an orbital are called an electron pair.