![]() ![]() This module describes the first important ‘quantum model’ of the atom and some of the evidence that supported it. The overthrow of this ‘planetary model’ of the atom – still the most advanced model that most non–physicists meet – raised the problem of understanding the internal structure of atoms to one of crucial importance and opened the way for the development of other models of atomic structure that called on ideas from the new field of quantum physics. In particular, his suggestion that each atom was like a miniature Solar System, in which the electrical force held the electrons in orbit around the nucleus in much the same way that gravitational forces bind the planets to the Sun, was soon shown to be inconsistent with the laws of physics as they were then known. The concept of the atomic nucleus quickly gained widespread acceptance, but some of Rutherford’s other ideas about the structure of atoms did not fare so well. the nuclei of helium atoms) were observed to rebound or scatter from gold atoms in thin metal foils. The presence of a nucleus at the heart of every atom was proposed in 1911 by Ernest_RutherfordErnest (later Lord) Rutherford (1871–1937) on the basis of experiments in which α–particles (i.e. The centrally located nucleus has a diameter of about 10 −14 m and occupies less than one trillionth (10 −12) of an atom’s volume, yet it contains more than 99.9% of its mass. A typical atom has a diameter of about 10 −10 m and consists of one or more negatively charged electrons moving under the electrical attraction of a small, dense, positively charged nucleus. The hundred or so different kinds of atom are the basic building blocks of all of the familiar forms of matter. Flame microsampling is accomplished using a micropipet to place 50–250 μL of sample in a Teflon funnel connected to the nebulizer, or by dipping the nebulizer tubing into the sample for a short time.1 Opening items 1.1 Module introduction 1.2 Fast track questions 1.3 Ready to study? 2 The production of atomic spectra 2.1 Characteristic emission spectra 2.2 Continuous emission spectra the black–body spectrum 2.3 Absorption spectra 2.4 Summary of Section 2 3 The emission spectrum of atomic hydrogen 3.1 The visible spectrum of atomic hydrogen Balmer’s formula 3.2 The ultraviolet and infrared series of spectral lines for hydrogen 3.3 Summary of Section 3 4 Bohr’s model for the hydrogen atom 4.1 The four postulates 4.2 Derivation of the allowed orbital radii 4.3 Derivation of the electron’s orbital speed 4.4 Derivation of the kinetic, potential and total energies of an electron 4.5 The energy level diagram for atomic hydrogen unbound states and ionization 4.6 Transitions, spectral lines and Balmer’s formula 4.7 Bohr’s model for the other series in the hydrogen spectrum 5 Production of spectra excitation by heating and by collisions 6 Closing items 6.1 Module summary 6.2 Achievements 6.3 Exit test For example, continuously aspirating a sample that has a high concentration of dissolved solids-sea water, for example, comes to mind-may build-up a solid de- posit on the burner head that obstructs the flame and that lowers the absorbance. Continuous aspiration is sample intensive, typically requiring from 2–5 mL of sample.įlame microsampling allows us to introduce a discrete sample of fixed volume, and is useful if we have a limited amount of sample or when the sample’s matrix is incompatible with the flame atomizer. ![]() The most common means for introducing a sample into a flame atomizer is a continuous aspiration in which the sample flows through the burner while we monitor absorbance. The relative size of each zone depends on many factors, including the choice of fuel and oxidant, and their relative proportions. Profile of typical flame using a slot burner.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |