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
26、avior of heat capacities Bohr model on the structure of hydrogen atom Compton scattering (x-ray scattering from electrons in a carbon target) Scientists always had trouble describing the nature of light is it a wave or is it a particle? In 1924, de Broglie reasoned that if light can have both wave a
27、nd particle properties, why not matter? From Einsteins relativistic energy equation, the energy of a particle with zero rest mass is the product of its momentum and the speed of light, E = pc Coupling this equation with the energy of a photon, E = h, reveals the de Broglie wavelength relationship, =
28、 h/p, which de Broglie asserted held for particles as well as photonsQuantum Mechanics and Molecular ThermodynamicsWaveParticle Duality The consequences of this relationship are far reaching (they led Schrdinger to his theory of wave mechanics), but its basis in nature is unquestionable Electron dif
29、fraction was observed by Davisson and Germer (1925) and G. P. Thomson (1927) The wavelike property of electrons is used in electron microscopes The wavelengths of the electrons can be controlled through an applied voltage, and the small de Broglie wavelengths offer a far more precise probe than an o
30、rdinary light microscope In addition, in contrast to electromagnetic radiation of similar wavelengths, the electron beam can be readily focused using electric and magnetic fieldsQuantum Mechanics and Molecular ThermodynamicsWaveParticle Duality In 1927, a year after presenting his theory of matrix m
31、echanics, Heisenberg stated one of the most provocative ideas in modern science the so-called uncertainty principle The Heisenberg uncertainty principle states that it is not possible to determine simultaneously to infinite precision of the momentum and the position of a particle Instead, the produc
32、t of the uncertainty in the momentum with the uncertainty in the position is given by the following relationQuantum Mechanics and Molecular ThermodynamicsThe Heisenberg Uncertainty Principle2 xpx The uncertainty principle is not a statement about the inaccuracy of measurement instruments, nor a refl
33、ection on the quality of experimental methods; it arises from the wave properties inherent in the quantum-mechanical description of nature Further, the uncertainty principle invalidates the Bohr model one cannot know the radius and angular momentum of an electron in a circular orbit with infinite pr
34、ecisionQuantum Mechanics and Molecular ThermodynamicsThe Heisenberg Uncertainty PrincipleChapter 2. The Foundation of Modern ChemistryChemistry: Atoms and Molecules Chemistry was originated from experiments Explanations on chemical phenomena were largely empirical Chemistry is a science about atoms
35、and molecules Chemical phenomena are dictated by electronic motion Quantum mechanics accurately describes electronic motion and nuclear motionFoundation of Modern Chemistry Virtually, all atoms, molecules and chemical processes can be described by quantum mechanics For heavy atoms, e.g. Au, elements
36、 in lanthanide series, relativistic theory should also be used due to the fast electronic motionQuantum Mechanics The entire quantum chemistry is about Eq. (2). Almost all the chemical phenomena can be explained by solving this equation.Electronic Structure of Atoms The electronic structures of othe
37、r atoms are similar but differ in energy levels and electron occupationElectronic Structure of AtomsTitanium (Ti)Gold (Au)Molecular Orbitals A molecular orbital is a linear combination of atomic orbitals of the constituent atoms The electronic energies of a molecule are quantized applications to pho
38、tochemistry, solar cells, etc.Chemical Bonding Covalent bond: electrons are shared between atoms (not necessarily equal) Ionic bond: electron from one atom is attached to another atomCONaClMolecular Interactions Covalent interactions (bonds) Electrostatic interactions (e.g. ionic bonds) Multipole in
39、teractions (e.g. dipole-dipole) van der Waals interactions (weak) Hydrogen bonding interactions (e.g. water)Potential Energy SurfaceSchematic of a potential energy landscape. At high temperatures (red line) the system is able to overcome potential energy barriers and sample many different basins. An
40、 energy minimization is shown with the black line: an equilibrium configuration is mapped via steepest descent to a local minimum on the landscape.Molecular StructureThe equilibrium structures correspond to the minima of the potential energy surfacesMolecular VibrationC-C StretchC-C WaveC-H StretchO
41、-H StretchThermodynamics Molecular internal energy (U) constituents: Electronic energy Vibrational energy Rotational energy Translational energy Enthalpy: H = U + PV Entropy (S): a measure of disorder in a thermodynamic system Gibbs free energy: G = H - TSChemical Kinetics-20-1001020304050Energy (kc
42、al/mol)Reaction CoordinatesRTEaAek/Arrhenius equation: the dependence of the rate constant k of chemical reactions on temperature T and activation energy Ea Molecular Spectroscopy UV/visible IR/Raman NMR MSphotoelectron spectrumvibrational spectrum XRD Photoelectron spectroscopy AFM/STM/SEM/TEMChapt
43、er 3. States of MatterStates of Matter Classical: gas liquid solid Non-classical: glass superfluid plasmaMacroscopically, the equilibrium states can be described by thermodynamics and statistical mechanics. However, the detailed microscopic processes can only be described by quantum mechanics.Gases
44、Ideal gas model: Non ideal gas model:nRTPV nRTnbVVaP)(2van der Waals equationCondensed Matter Substances Liquids: many chemical reactions occur in liquid phase interactions between molecules are stronger than in the gas phase molecules are solvated Solids: many compounds exist in solid forms and rea
45、ctions could occur among solid materials interatomic/intermolecular interactions varyClusters and Nano-Sized Materials Evolution of small clustersSolidsgraphite molecular solid semiconductor metalClusters and Nano-Sized MaterialsMolecular Orbitals vs. Energy Bands-15-10-505Orbital Energy (eV)CH2=CH2
46、H(CH=CH)2HH(CH=CH)3HH(CH=CH)4HH(CH=CH)2HH(CH=CH)5HH(CH=CH)6HDOS(4x4x1)non-metallic metallicprimitive cellelectron density differencegraphiteBand StructureFermi Energy and Fermi-Dirac Distribution/ )exp(11)(kTEEEfFpuren-dopingp-dopingChapter 4. Chemistry, Chemical Engineering and Materials ScienceHom
47、ogeneous Catalysis Production of fine chemicals Chiral synthesisHeterogeneous Catalysis NOx reduction Petrochemical refinery Hydrogen production Biomass reformingSemiconductors Band gap: the energy difference between a conduction band and a valence band A typical semiconductor band gap is below 3 eV
48、 The widely utilized semiconductors include Si, SiC, SiN, GaAs, Ge, InAs, etc.Copper Deposition on SiCu Thin Film: Current TechnologyIMDIMDPVD TaN Diffusion BarrierPVD Ta Glue LayerPVD Cu Copper SeedECP CuCVD: CupraSelectTM on Ta(100)ab initio MDsimulation200oC4 psCupraSelectTM on TaN(111) & WN(111)
49、TaN(111) WN(111)Cu Agglomeration on TaN(111)Cu Agglomeration on TaN(111)Ru Glue LayerElectron Density DifferenceTaNWNWithout Ru glue layerWith Ru glue layerCuCuSuperconductors A compound conducting electricity without resistance below a certain temperature Superconductors: Pb (7.2K) Nb3Ge (23.2K) Ca
50、SrCu2O4 (110K) (Sn5In)Ba4Ca2Cu10Oy (212K) (Tl5Pb2)Ba2MgCu10O17+ (18oC, world record!)magnetic-levitation MRI imaging energy storageChemistry and Energy Materials Hydrocarbon reforming Biomass, coal fire gasification, municipal waste treatment Solar cells Energy level alignment Energy storage Li-ion
