《基础化学》英文教学课件：chapter-9

1、Chapter 9. Structure of Atoms and Periodic Table of the Elements 9-1. Fundamentals 9-2. Structure of Hydrogen Atom 9-3. Quantum Numbers and Atomic Orbitals 9-4. Electron Configurations and PeriodicityHow are the electrons distributed in this space? what are the electrons doing in the atom?1. Fundame

2、ntals All matter is composed of indivisible atoms. An atom is an extremely small particle of matter that retains its identity during chemical reactions.Postulates of Daltons atomic theory (1803)Fe on Cu(111)Xe on Ni (110)Single atoms can be visualized and manipulated by scanning-tunneling microscope

3、 (STM, 扫描隧道显微镜).1. Fundamentals An element is a type of matter composed of only one kind of atom, each atom of a given kind having the same properties. Na, Cl2. A compound is a type of matter composed of atoms of two or more elements chemically combined in fixed proportions. NaCl, H2O. A chemical re

4、action consists of the rearrangement of the atoms present in the reactants to give new chemical combinations present in the products. Atoms are not created, destroyed, or broken into smaller particles by any chemical reaction.John Dalton 约翰道尔顿(1766-1844) England atomic theory1. Fundamentals1. Fundam

5、entalsJ. J. Thomson (18561940) English 约瑟夫汤姆逊Nobel Prize (Physics),1906Raisin bread model (1904)In 1897, Thomson discovered electrons, by which he proposed the raisin bread model (葡萄干面包模型) of atoms.Discovery of electronMarie Curie 玛丽居里 (1867-1934) Poland Nobel Prize (Physics),1903 (Chemistry),1911po

6、lonium, Po, 84 radium, Ra, 88 Henri Becquerel亨利贝克勒尔 (1852-1908) France Nobel Prize (Physics),1903Discovery of Radioactivity uranium, U, 92 1. FundamentalsWilliam Thomson, 1st Baron Kelvin 威廉汤姆森，第一代开尔文男爵(18241907) British 热力学之父William Thomson, 1st Baron Kelvin 威廉汤姆森，第一代开尔文男爵(18241907) British 热力学之父E.

7、 Rutherford欧内斯特卢瑟福(18711937) New Zealand Nobel Prize, 1908ChemistryDiscovery of protonFather of nuclear physics1. Fundamentals1. Fundamentals1. FundamentalsAn atom consists of two kinds of particles: a positively(+)-charged nucleus (10-15 m), which contains most (99.95%) of the atoms mass, and one o

8、r more electrons. An electron is a negatively(-)-charged particle that exists in the region (10-10 m) around the nucleus.Nuclear model (有核模型) (1911)1. FundamentalsStructure of an atom?How are the electrons distributed in this space?(What are the electrons doing in the atom?) According to Rutherfords

9、 model, an atom consists of a nucleus many times smaller than the atom itself, with electrons occupying the remaining space.Rutherfords model posed a dilemma.According to the nuclear model, an electron wouldcontinuously lose energy as electromagnetic radiation (photons);spiral into the nucleus (in a

10、bout 10-10 s).2. Structure of Hydrogen Atomcontinuous energy: continuous wavelength: continuous spectrum;the atom would “die”.http:/2. Structure of Hydrogen AtomI. Continuous vs. line spectrum (连续光谱和线状光谱)Dispersion of white light by a prism (棱镜): White light, entering at the left, strikes a prism, w

11、hich disperses the light into a continuous spectrum of wavelength.A heated solid (such as a heated tungsten filament (钨丝) emits light with continuous spectrum (a spectrum containing light of all wavelengths).2. Structure of Hydrogen AtomEmission line spectra of some elements: The lines corresponds t

12、o visible light (380780 nm) emitted by atoms. A heated gas (atom) emits light with line spectrum (a spectrum showing only certain colors or specific wavelengths of light).Hydrogen line spectraHelium line spectra2. Structure of Hydrogen Atom2. Structure of Hydrogen AtomIn 1885 J. J. Balmer showed tha

13、t the wavelengths in the visible spectrum of hydrogen could be reproduced by a simple formula:Here n is some whole number (integer) greater than 2. The wavelengths of the four lines in the hydrogen atom visible spectrum correspond to n = 3, 4, 5, and 6, respectively.Max Planck 马克斯普朗克 (18581947) Germ

14、anNobel prize, 1918PhysicsPlanck postulate Josiah Willard Gibbs威拉德吉布斯(18391903 ) USAGibbs entropy2. Structure of Hydrogen AtomE = n h2. Structure of Hydrogen AtomAlbert Einstein 阿尔伯特爱因斯坦 (1879-1955) Nobel prize, 1929PhysicsPhotoelectric effect2. Structure of Hydrogen AtomConsider this analogy to hel

15、p see why light of insufcient energy cannot free an electron from a metal surface. If one Ping-Pong ball does not have enough energy to knock a book off its shelf, neither does a series of Ping-Pong balls, because the book cannot save up the energy from the individual impacts.But one base-ball trave

16、ling at the same speed does have enough energy to move the book. Whereas the energy of a ball is related to its mass and velocity, the energy of a photon is related to its frequency.2. Structure of Hydrogen AtomII. The Bohr Theory of the Hydrogen Atom (1913)To account for:The stability of the hydrog

17、en atom (that the atom exists and the electron does not continuously radiate energy and spiral into the nucleus);The line spectrum of the atom.N. Bohr尼尔斯玻尔 (1885-1962)DenmarkNobel prize (1922)Bohr modelN. Bohr尼尔斯玻尔 (1885-1962)DenmarkNobel prize (1922)2. Structure of Hydrogen Atom1. Energy-level post

18、ulate:An electron can have only specific energy values in an atom, which are called its energy levels (能级).http:/www. ground state (基态)excited states(激发态)n: principal quantum number(主量子数)2. Structure of Hydrogen AtomThe energies have negative values because the energy of the separated nucleus and el

19、ectron is taken to be zero. As the nucleus and electron come together to form a stable state of the atom, energy is released and the energy becomes less than zero, or negative.The first postulate explains the stability of hydrogen atoms.2. Structure of Hydrogen Atom2. Structure of Hydrogen Atom2. Tr

20、ansitions (跃迁) between energy levels:An electron in an atom can change energy only by going from one energy level to another energy level. By doing so, the electron undergoes a transition.The second postulate explains the line spectrum emitted by hydrogen atoms.http:/2. Structure of Hydrogen AtomExp

21、laining the line spectrum emission by atomsAn electron in a higher energy level (initial energy level Ei) undergoes a transition to a lower energy level (final level Ef).2. Structure of Hydrogen AtomExample 9-1: What is the wavelength of light emitted when the electron in a hydrogen atom undergoes a

22、 transition from energy level n = 4 to level n = 2?Solution:(blue-green)2. Structure of Hydrogen AtomBalmer series (visible):Paschen series (infrared):Lyman series (ultraviolet):2. Structure of Hydrogen AtomThe nucleus is composed of two different kind of particles, protons (质子), and neutrons (中子).N

23、uclear composition (1932)Subatomic Particles2. Structure of Hydrogen AtomJ. Chadwick詹姆斯查德威克(18911974)Nobel Prize,1935PhysicsDiscovery of the neutron2. Structure of Hydrogen AtomEvaluation of Bohrs theorySuccess: The theory firmly established the concept of atomic energy level. It can account for (1)

24、 the stability of the hydrogen atom and (2) the line spectrum of the atom.Limitation: The theory was unsuccessful, however, in accounting for the details of atomic structure and in predicting energy levels for atoms other than hydrogen. 2. Structure of Hydrogen AtomIII. Wave-particle duality (波粒二象性)

25、 of the electronAccording to Einstein, light has not only wave properties, which we characterize by frequency and wavelength, but also particle properties. For example, a particle of light, photon, has momentum. This momentum, mc, is related to the wavelength of the light:Relativistic mass2. Structu

26、re of Hydrogen AtomDe Broglie relation:Louis de Broglie reasoned that if light (considered as a wave) exhibits particle aspects, then perhaps particles of matter show characteristics of waves under the proper circumstances. He therefore postulated that a particle of matter of mass m and speed has a

27、wavelength, by analogy with light:L. de Broglie路易维克多德布罗意(1892-1987) FranceNobel prize(1929)Wave nature of electrons 2. Structure of Hydrogen AtomDe Broglie relation:An electron (9.110-31 kg) moving at about 5.9105 ms-1 has a wavelength of about 1.210-9 m.A basketball (0.60 kg) moving at about 10 ms-

28、1 has a wavelength of about 10-34 m.2. Structure of Hydrogen Atom2. Structure of Hydrogen AtomThey showed that electrons gave a diffraction pattern (衍射图) when reflected from a crystal or pass through a very thin gold foil. Both Thomson received Nobel prizes: J. J. for showing that the electron is a

29、particle and G. P. for showing that it is a wave.The wave property of electrons was demonstrated by C. Davisson, L. H. Germer and G. P. Thomson (son of J. J. Thomson).Ernst Ruska恩斯特鲁斯卡 (1906 1988) GermanNobel Prize, (1986) PhysicsElectron Microscopy E. Ruska used this wave property to construct the

30、first electron microscope (电子显微镜) in 1933. Shown is the scanning electron microscope image of a wasps head.2. Structure of Hydrogen Atom2. Structure of Hydrogen AtomYou cannot say that the electron will definitely be at a particular position at a given time, we can say that the electron is likely to

31、 be at this point.Wave property of electrons: Statistical statements about where we would find the electron (probability of finding an electron at a certain point in an atom).2. Structure of Hydrogen AtomDe Broglie relation says that electrons can not be treated only as particles. In some circumstan

32、ces, they demonstrate wave properties, which must be considered to uncover the atomic structures.Significance of de Broglie relationIV. Uncertainty Principle2. Structure of Hydrogen AtomIt is impossible to know simultaneously, with absolute precision, both the position and the momentum of a particle

33、 such as an electron.W. Heisenberg维尔纳海森伯(1901-1976) GermanyNobel prize(1932)Uncertainty Principle 2. Structure of Hydrogen AtomHeisenbergs uncertainty principle (测不准原理): The product of the uncertainty in position and the uncertainty in momentum of a particle can be no smaller than Planks constant di

34、vided by 4. x: The uncertainty in the x coordinate of a particle;px: The uncertainty in the momentum in the x direction.If you know very well where a particle is, you can not know where it is going !2. Structure of Hydrogen AtomFor an electron with a velocity of 6.0106 ms-1 (an error of 1%):For a ba

35、sketball with a velocity of 10 ms-1 (an error of 1%)The uncertainty principle is only significant for particles of very small mass such as electrons.2. Structure of Hydrogen AtomHeisenbergs uncertainty principle says that, for electrons, the uncertainties in position and momentum are normally quite

36、large. We can not describe the electron in an atom as moving in a definite orbit.Significance of uncertainty principleV. Wave Function（波函数）2. Structure of Hydrogen AtomIn 1926, E. Schrdinger devised a theory (Schrdinger equation) that could be used to find the wave properties of electrons in atoms a

37、nd molecules.E. Schrdinger埃尔文薛定谔(1887-1961) AustriaNobel prize(1933)De broglies relation applies quantitatively only to particles in a force-free environment. It cannot be applied directly to an electron in an atom, where the electron is subject to the attractive force of the nucleus. Schrdinger equ

38、ation 2. Structure of Hydrogen Atom2. Structure of Hydrogen AtomInformation about an electron in an atom is contained in a mathematical expression called wave function, denoted by the Greek letter, . The wave function is obtained by solving Schrdinger equation:2, gives the probability of finding an

39、electron within a region of space. The diagram shows the probability density (概率密度) (at a point) for an electron in a hydrogen atom in the ground state.2. Structure of Hydrogen Atom2. Structure of Hydrogen Atom2. Structure of Hydrogen AtomThe graph shows the probability (概率) (within a spherical shel

40、l) of finding the electron within shells at various distances from the nucleus. The curve exhibits a maximum (r= 52.9 pm, Bohr radius), which means that the radial probability is greatest for a given distance from the nucleus. Probability2. Structure of Hydrogen AtomInformation about an electron in

41、an atom is contained in a wave function, which can just be obtained by solving me under specific conditions. Solve me, and you get everything the states of electrons in an atom.Significance of Schrdinger Equation3. Quantum Numbers and Atomic OrbitalsInformation about an electron in an atom is contai

42、ned in a wave function, , which gives the probability of finding the electron at various points in space.Three different quantum numbers are needed because there are three dimensions to space.A group of wave functions is obtained by solving Schrdinger equation. For solving Schrdinger equation, three

43、 integral conditions must be satisfied. These integers n, l, m are referred as quantum numbers.(n, l, m) specify a wave function, n,l,m. 3. Quantum Numbers and Atomic OrbitalsA wave function for an electron in an atom is called an atomic orbital (原子轨道). Probability density for an electron in a hydro

44、gen atom in the ground state.An atomic orbital is pictured qualitatively by describing the region of space where there is high probability (99%) of finding the electrons. The atomic orbital so pictured has a definite shape.I. Quantum numbers3. Quantum Numbers and Atomic Orbitals1. Principal quantum

45、number (n，主量子数) The smaller n is, the lower the energy. In the case of the hydrogen atom (single electron), n is the only quantum number determining the energy. For other atoms, the energy also depends to a slight extent on the l quantum number.General meaning:This quantum number is the one on which

46、 the energy of an electron in an atom principally depends; it can have any positive integer value: 1, 2, 3, and so on.3. Quantum Numbers and Atomic Orbitals n also determines the average distance of electron to the nucleus or the size of an orbital. The larger the value of n is, the larger the orbit

47、al, or the farer the distance of an electron to the nucleus. Orbitals of the same quantum state n are said to belong to the same shell (层). Shells are sometimes designated by the following letters:LetterKLMNOPQn12345673. Quantum Numbers and Atomic Orbitals2. Angular momentum quantum number (l, 角动量量子

48、数)This quantum number distinguish orbitals of given n having different shapes, it can have any integer value from 0 to n-1. n = 1: l = 0 n = 2: l = 0, 1 n = 3: l = 0, 1, 2 n = 4: l = 0, 1, 2, 3 3. Quantum Numbers and Atomic OrbitalsLetterspdfl0123 Orbitals of the same n but different l are said to b

49、elong to different subshells (亚层) of a given shell. The different subshells are usually denoted by letters as follows:The choice of letter symbols for quantum numbers survives from old spectroscopic terminology (describing the lines in a spectrum as sharp, principal, diffuse, and fundamental). 3. Qu

50、antum Numbers and Atomic OrbitalsTo denote a subshell within a particular shell, we write the value of the n for the shell, followed by the letter designation for the subshell. For example, 2p denotes a subshell with quantum numbers n = 2 and l = 1. The energy of an orbital also depends somewhat on

51、the l quantum number (except for the H atom). For a given n, the energy of an orbital increases with l.3d? 4f?energy (n,l) Within each shell of quantum number n, there are n different kinds of orbitals, each with a distinctive shape denoted by an l quantum number. 3. Quantum Numbers and Atomic Orbit

52、alsn=1: l=0(s); 1s.n=2: l=0(s), 1(p); 2s, 2p.n=3: l=0(s), 1(p), 2(d);3s, 3p, 3d.3. Quantum Numbers and Atomic Orbitals3. Magnetic quantum number (m, 磁量子数)This quantum number distinguish orbitals of given n and lthat is, of given energy and shape but having a different orientation in space; the allow

53、ed values are the integers from l to l. Every value denotes an individual atomic orbital.l = 0 (s): m = 0;There is only one orbital in the s subshell.3. Quantum Numbers and Atomic Orbitalsl = 1 (p): m = -1, 0, 1;There are three different orbitals in the p subshell.l = 2 (d): m = -2, -1, 0, 1, 2; The

54、re are five different orbitals in the d subshell.There is no direct relation between the values of m and the x, y, z designation of the orbitals.3. Quantum Numbers and Atomic OrbitalsNote that there are 2l+1 orbitals in each subshells of quantum number l. These orbitals have the same shape and energ

55、y, though with different orientation in space, thus called equivalent orbital (等价轨道).3. Quantum Numbers and Atomic Orbitals4. Spin quantum number (ms, 自旋量子数)This quantum number refers to the two possible orientation of the spin axis of an electron; possible values are +1/2 and 1/2. 3. Quantum Number

56、s and Atomic OrbitalsThe first three quantum numbers characterize the orbital that describe the region of space where an electron is most likely to be found; we say that the electron “occupies” this orbital. The spin quantum number describes the spin orientation of the electron.Each electron in an a

57、tom has four different quantum numbersthe principal quantum number (n), the angular momentum quantum number (l), and the magnetic quantum number (m), the spin quantum number (ms).3. Quantum Numbers and Atomic Orbitals3. Quantum Numbers and Atomic OrbitalsPermissible Values ofQuantum Numbers for Atom

58、ic Orbitals3. Quantum Numbers and Atomic OrbitalsExample 9-2: State whether each of the following sets of quantum numbers is permissible for an electron in an atom. If a set is not permissible, explain why.Solution:a. n = 1, l = 1, m = 0, ms =b. n = 3, l = 1, m = -2, ms =c. n = 2, l = 1, m = 0, ms =

59、d. n = 2, l = 0, m = 0, ms = 1Not permissible. The l is equal to n; it must be less than n.Not permissible. The magnitude of the m (that is, the m value, ignoring it sign) must not be greater than l.Permissible.Not permissible. The ms can be only +1/2 or 1/2.3. Quantum Numbers and Atomic OrbitalsThe

60、 electron in a 2s orbital is likely to be found in two regions, one near the nucleus and the other in a spherical shell about the nucleus (the electron is most likely to be here). II. Atomic orbital shapesCross sectional representations and cutaway diagrams of the probability distributions of a 1s a