无机化学课件:A+Brief+Introduction+to+Modern+Chemistry.2.ppt
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- 无机化学 课件 Brief Introduction to Modern Chemistry
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1、A Brief Introduction to Modern ChemistryHansong ChengChapter 1. Fundamentals Chemistry: A Core Science Chemistry and physics (physical sciences) Chemistry and biology (life science) Chemistry and materials (materials science) Chemistry and chemical engineering (engineering science) Chemistry and nan
2、otechnology Chemistry and environmental scienceScience and ScientistsScientists, contrary to the myth that they themselves publicly promulgate, are emotional human beings who carry a generous dose of subjectivity with them into the supposedly objective search for The Truth. The anonymous aphorism, I
3、 wouldnt have seen it if I hadnt believed it is a continuing truth in science. And of course, it cuts two ways: you often see what you expect to see and not what you dont. Science: objective Scientists: subjectiveScience writer and Evolutionist Roger Lewin:Science Learning and Scientific Research Cl
4、assroom learning: Passive Learning what has been already discovered Knowledge building Scientific research: Proactive Discovery of unknowns Experience buildingScience and Scientific Methods Empirical observations Identification of key issues Background search Establishment of a scientific model Iden
5、tify the key characteristic phenomena Simplify the model by eliminating unimportant characteristics and defining the limit of the model Scientific proofs (experiments) Mechanisms Communications Interacting with each other PresentationsScientific Ethics Honesty in reporting of scientific data; Carefu
6、l transcription and analysis of scientific results to avoid error; Independent analysis and interpretation of results that is based on data and not on the influence of external sources; Open sharing of methods, data, and interpretations through publication and presentation; Sufficient validation of
7、results through replication and collaboration with peers; Proper crediting of sources of information, data, and ideas; Moral obligations to society in general, and, in some disciplines, responsibility in weighing the rights of human and animal subjects From: http:/ Physical SciencesToward the end of
8、 the 19th century many physicists held that all the principles of physics had been discoveredNewtons mechanics had been brought to a high degree of sophistication by the work of Lagrange and HamiltonThe equivalence of heat and mechanical work had been clearly demonstrated by Count Rumford and JouleC
9、lassical PhysicsThe complete development of thermodynamics had been formulated by Gibbs, which remains unchanged todayThe kinetic theory of gases and statistical mechanics had been refined to a high degree by Maxwell, Boltzmann and GibbsIn the field of optics, the work of Young and Fresnel on interf
10、erence phenomena had resulted in the acceptance of the wave theory of light (Huygens) over the corpuscular theory of light (Newton)Quantum Mechanics and Molecular ThermodynamicsClassical Physics The unification of optics, electricity and magnetism within Maxwells equations of the electromagnetic nat
11、ure of lightQuantum Mechanics and Molecular ThermodynamicsThe body of these accomplishments is now considered to be the development of what we now refer to as classical physics.Classical PhysicsThe Discovery of Electrons In the late 19th century, it became possible to seal metal electrodes within a
12、glass tube and then evacuate the tube to very low pressures Before evacuation, an increase in voltage across the electrodes results in a spark As the pressure is lowered, the sparking is replaced by a luminous beamSir John J. Thomson In 1897, J. J. Thomson demonstrated that the beam that leaves the
13、cathode consists of negatively charged discrete particles By balancing the beam between an electric and magnetic field, Thomson was able to measure the charge-to-mass ratio of these particles Thus he showed that an electron was lighter than the lightest atomQuantum Mechanics and Molecular Thermodyna
14、micsThe Discovery of ElectronsThis discovery of a subatomic particle together with the discovery of X-rays by Rentgen in 1895 and radioactivity by Becquerel in 1896 showed that the atom was far more complex than previously thought. The series of experiments that revolutionised the concepts of physic
15、s had to do with the radiation given off by material bodies when heated As a body is heated to higher and higher temperatures there is a continual shift of colour from red through white to blue The exact spectrum emitted by a body depends on the particular body itself, but an ideal body, one that ab
16、sorbs and emits radiation without favouring particular frequencies, is called a blackbody radiatorQuantum Mechanics and Molecular ThermodynamicsBlackbody RadiationQuantum Mechanics and Molecular ThermodynamicsBlackbody RadiationThe Quantum Hypothesis The first person to offer a successful explanatio
17、n of blackbody radiation was Planck in 1900 Like Rayleigh and Jeans, Planck assumed that the radiation emitted by the body was due to the oscillations of the electrons within the medium Planck made the revolutionary Quantum Mechanics and Molecular Thermodynamicsad hoc assumption that the energies of
18、 the oscillators had to be proportional to an integral multiple of the frequency, i.e. n = nh, where n is an integer and h is a proportionality constant The photoelectric effect discovered by Hertz is the ejection of electrons from metallic surfaces when illuminated by electromagnetic radiation The
19、experimental data showed that the energy of the ejected electrons was proportional to the frequency of the illuminating light The fact that the ejection energy was independent of the total energy of illumination implied that the interaction must be like that of a particle which gives all its energy
20、to the electronQuantum Mechanics and Molecular ThermodynamicsThe Photoelectric EffectQuantum Mechanics and Molecular Thermodynamics Three important results need to be explained:1. No electrons are ejected , regardless of the intensity of the radiation, unless the frequency exceeds a threshold value
21、characteristic of the metal2. The kinetic energy of the ejected electrons is linearly proportional to the frequency of the incident radiation but independent of its intensity3. Even at low light intensities, electrons are ejected immediately if the frequency is above the thresholdThe Photoelectric E
22、ffect To explain these results, Einstein extended Plancks hypothesis in an important way Planck applied the energy quantisation concept = h, to the emission and absorption mechanism of atomic electronic oscillators Planck believed that once the light energy was emitted, it behaved like a classical w
23、ave Einstein proposed instead that radiation itself existed as small packets of energy, = h, which are now known as photonsThe Photoelectric EffectAlbert EinsteinQuantum Mechanics and Molecular Thermodynamics Using conservation of energy, the kinetic energy of the emitted electrons is equal to the e
24、nergy of the incident radiation minus the minimum energy required to remove an electron from the surface of the particular metal () the work function hmv221 If h emission will occur even at low intensity (satisfies 3)The Photoelectric EffectThe slope of the photoelectric data gives a value of h in c
25、lose agreement with Plancks value deduced from blackbody radiation. In two very different sets of experiments, blackbody radiation and the photoelectric effect, the very same quantisation constant, h, arose naturally.The Photoelectric EffectOther Crisis of Classical Physics Temperature dependent beh
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