Investigations of Spectra
Text 35 A Investigations of Spectra - раздел Образование, Part One THE PREDICATE The More Profound Is The Investigation Of The Structure Of Atoms And Molcculc...
The more profound is the investigation of the structure of atoms and molcculcs, the more problems arise. It was not long ago that consideration
of the cxtra-nuclcar clcctrons was rcstrictcd to an indication (hat their number must equal the atomic number of the clement, and to a mention of the fact that they form a relatively open structure about the ccntral nucleus. The question of their arrangement must now be discusscd in detail, and in this conncction valuable information has been obtained from an examination of both optical and X-ray spectra, the former term being used to describe spectra in the ultraviolet, visible and infra-red regions.
When a solid is heated to incandcsccncc, it emits a more or less continuous spcctrum, but gases and vapours under the same conditions, when examined spcctroscopically, show a series often very complicated, of distinct lines or bands occupying definite positions, diat is, with definite wave lengths. The more information conccrning the composition of various spectra was obtained, the clearer it became that the line spectra arc produced by atoms and so arc not unfrcqucntly referred to as atomic spectra, whereas the so-called band spectra, which can, in fact, often be resolved into large number of closely spaccd lines, arc obtained from molcculcs.
A line spectrum is the one formed when radiation from an incandescent gas is passed through a slit and then dispersed. The lines arc produced by energy changcs when electrons pass from high energy quantum levels to low energy quantum levels. The clcctrons arc cxcitcd from low to high levels by the input of energy into the gas — usually in a discharge tube under a high voltage.
In a molecular spcctrum, a scries of fairly broad bands is formed. These bands arc sharp at one edge but dying away on the other. They arise from the complex energy changcs possible in a molcculc. Under high resolution, the band is shown to be made up of many lines sharper and clcarcr together at the head of the band but more diffuse away from the head of the band. It seems not at all unlikely that the more complcx the molcculc, the more complicated the spcctrum is.
It is from atomic spcctra in particular diat information conccrning the cxtra-nuclcar electrons has been obtained.
