So far we have focused our attention on the motions of the single electron in the hydrogen atom. We now consider atoms which more than one electron and we examine the motions of electrons that lie deep binding energy and we examine the motions of electrons that lie deep within such atoms. We move from a region of relatively low binding energy (5 eV for the work required to remove the valence electron from sodium, for example) to a region of higher binding energy (70 ke V to remove a n innermost electron from tungsten, for example) although still part of the electromagnetic spectrum, the radiations emitted by such deep seated electrons differ drastically in wavelength for example, from ~ 6 X 10^-7 m for the sodium doublet lines to ~2 X 10^-11 m for one of the tungsten characteristic radiation, a ratio of about 3 X 10⁴. Radiation of such short wavelength falls in the x-ray region of the spectrum. The wavelength spectrum of the x ray produced when 35-keV electrons are allowed to strike a molybdenum target.