Chapter 6 Electronic Structure of Atoms

Transcription

1 Sec$on 7.1 Electromagne,c Radia,on Chapter 6 Electronic Structure of Atoms

2 Sec$on 7.1 Electromagne,c Radia,on Different Colored Fireworks Copyright Cengage Learning. All rights reserved 2

3 Sec$on 7.1 Electromagne,c Radia,on Ques$ons to Consider Why do we get colors? Why do different chemicals give us different colors? Copyright Cengage Learning. All rights reserved 3

4 Sec$on 7.1 Electromagne,c Radia,on Electromagne$c Radia$on One of the ways that energy travels through space. Three characteris$cs: Wavelength Frequency Speed Copyright Cengage Learning. All rights reserved 4

5 Sec$on 7.1 Electromagne,c Radia,on Characteris$cs Wavelength ( λ) distance between two consecu$ve peaks or troughs in a wave. Frequency ( ν ) number of waves (cycles) per second that pass a given point in space Speed (c) speed of light ( m/s) c = λν Copyright Cengage Learning. All rights reserved 5

6 Sec$on 7.1 Electromagne,c The Nature of Waves Radia,on 6

7 Sec$on 7.1 Electromagne,c Radia,on Classifica$on of Electromagne$c Radia$on Copyright Cengage Learning. All rights reserved 7

8 Sec$on 7.2 The Nature of Ma7er Pickle Light Copyright Cengage Learning. All rights reserved 8

9 Sec$on 7.2 The Nature of Ma7er Energy can be gained or lost only in whole number mul$ples of. hν A system can transfer energy only in whole quanta (or packets ). Energy seems to have par$culate proper$es too. Copyright Cengage Learning. All rights reserved 9

10 Sec$on 7.2 The Nature of Ma7er Energy is quan$zed. Electromagne$c radia$on is a stream of par$cles called photons. = = hc Ephoton hν λ Planck s constant = h = Js Copyright Cengage Learning. All rights reserved 10

11 Sec$on 7.2 The The Nature Photoelectric of Ma7er effect Light has both: 1. wave nature 2. particle nature Photon is a particle of light hν KE e - Kinetic energy of one electron (KE): KE = ½ mv 2 = hν hν 0 Copyright Cengage Learning. All rights reserved 11

12 Sec$on 7.2 The Nature of Ma7er Energy has mass E = mc 2 Dual nature of light: Electromagne$c radia$on exhibits wave proper$es and par$culate proper$es. Dual nature of par$cles, such as electrons: Electrons exhibits both wave and par$culate proper$es. λ = h / mv Copyright Cengage Learning. All rights reserved 12

13 Sec$on 7.3 The Atomic Spectrum of Hydrogen The Atomic Spectrum of Hydrogen Con$nuous spectrum (results when white light is passed through a prism) contains all the wavelengths of visible light Line spectrum each line corresponds to a discrete wavelength: Hydrogen emission spectrum Copyright Cengage Learning. All rights reserved 13

14 Sec$on 7.3 The Hydrogen Atomic Emission Spectrum Spectrum of Hydrogen Copyright Cengage Learning. All rights reserved 14

15 Sec$on 7.3 The Atomic Spectrum of Hydrogen Significance Only certain energies are allowed for the electron in the hydrogen atom. Energy of the electron in the hydrogen atom is quan$zed. Copyright Cengage Learning. All rights reserved 15

16 Sec$on 7.4 The Bohr Model The Bohr Model Electron in a hydrogen atom moves around the nucleus only in certain allowed circular orbits. Bohr s model gave hydrogen atom energy levels consistent with the hydrogen emission spectrum. Ground state lowest possible energy state (n = 1)

17 Sec$on 7.4 The Bohr Model Electronic Transi$ons in the Bohr Model for the Hydrogen Atom a) An Energy-Level Diagram for Electronic Transi$ons Copyright Cengage Learning. All rights reserved 17

18 Sec$on 7.4 The Bohr Model Electronic Transi$ons in the Bohr Model for the Hydrogen Atom b) An Orbit-Transi$on Diagram, Which Accounts for the Experimental Spectrum Copyright Cengage Learning. All rights reserved 18

19 Sec$on 7.4 The Bohr Model The Bohr Model For a single electron transi$on from one energy level to another: ΔE = J 2 2 nfinal ninitial ΔE = change in energy of the atom (energy of the emihed photon) n final = integer; final energy level n ini$al = integer; ini$al energy level Copyright Cengage Learning. All rights reserved 19

20 Sec$on 7.4 The Bohr Model The model correctly fits the quan$zed energy levels of the hydrogen atom and postulates only certain allowed circular orbits for the electron. As the electron becomes more $ghtly bound, its energy becomes more nega$ve rela$ve to the zero-energy reference state (free electron). As the electron is brought closer to the nucleus, energy is released from the system. Copyright Cengage Learning. All rights reserved 20

21 Sec$on 7.4 The Bohr Model Bohr s model is incorrect: This model only works for hydrogen. Electrons move around the nucleus in circular orbits. Copyright Cengage Learning. All rights reserved 21

22 Sec$on 7.5 The Heisenberg Quantum Uncertainty Mechanical Principle Model of the Atom We do not know the detailed pathway of an electron. Heisenberg uncertainty principle: There is a fundamental limita$on to just how precisely we can know both the posi$on and momentum of a par$cle at a given $me. Δx = uncertainty in a par$cle s posi$on Δ(mν) = uncertainty in a par$cle s momentum h = Planck s constant ( m ) Δx Δ ν h 4π Copyright Cengage Learning. All rights reserved 22

23 Sec$on 7.5 The Quantum Mechanical Model of the Atom Physical Meaning of a Wave Func$on (Ψ) The square of the func$on indicates the probability of finding an electron near a par$cular point in space. Probability distribu$on intensity of color is used to indicate the probability value near a given point in space. Copyright Cengage Learning. All rights reserved 23

24 Sec$on 7.5 The Quantum Mechanical Model of the Atom Probability Distribu$on for the 1s Wave Func$on Copyright Cengage Learning. All rights reserved 24

25 Sec$on 7.5 The Quantum Mechanical Model of the Atom Radial Probability Distribu$on Copyright Cengage Learning. All rights reserved 25

26 Sec$on 7.5 The Quantum Mechanical Model of the Atom Rela$ve Orbital Size Difficult to define precisely. Orbital is a wave func$on. Picture an orbital as a three-dimensional electron density map. Hydrogen 1s orbital: Radius of the sphere that encloses 90% of the total electron probability. Copyright Cengage Learning. All rights reserved 26

27 Sec$on 7.6 Quantum Numbers Each orbital is characterized by a series of numbers called quantum numbers: Principal quantum number (n) size and energy of the orbital. Angular momentum quantum number (l) shape of atomic orbitals (some$mes called a subshell). Magne$c quantum number (m l ) orienta$on of the orbital in space rela$ve to the other orbitals in the atom.

28 Sec$on 7.6 Quantum Numbers for the First Four Levels of Orbitals in the Hydrogen Atom

29 Sec$on 7.7 Orbital Shapes and Energies Three Representa$ons of the Hydrogen 1s, 2s, and 3s Orbitals Copyright Cengage Learning. All rights reserved 29

30 Sec$on 7.7 Orbital Shapes and Energies 1s, 2s and 3s Orbitals l = 0 (s orbitals) Copyright Cengage Learning. All rights reserved 30

31 Sec$on 7.7 Orbital Shapes and Energies 2p Orbitals n = 2, l = 1 Copyright Cengage Learning. All rights reserved 31

32 Sec$on 7.7 Orbital Shapes and Energies The Boundary Surface Representa$ons of All Three 2p Orbitals Copyright Cengage Learning. All rights reserved 32

33 Sec$on 7.7 Orbital Shapes and Energies 3d Orbitals n = 3, l = 2 Copyright Cengage Learning. All rights reserved 33

34 Sec$on 7.7 Orbital Shapes and Energies The Boundary Surfaces of All of the 3d Orbitals Copyright Cengage Learning. All rights reserved 34

35 Sec$on 7.7 Orbital Shapes and Energies Representa$on of the 4f Orbitals in Terms of Their Boundary Surfaces Copyright Cengage Learning. All rights reserved 35

36 Sec$on 7.8 Electron Spin and the Pauli Principle Electron Spin Electron spin quantum number (m s ) can be +½ or -½. Pauli exclusion principle - in a given atom no two electrons can have the same set of four quantum numbers. An orbital can hold only two electrons, and they must have opposite spins. Copyright Cengage Learning. All rights reserved 36

37 Sec$on 7.9 Polyelectronic Atoms Polyelectronic Atoms Atoms with more than one electron. Electron correla$on problem: Since the electron pathways are unknown, the electron repulsions cannot be calculated exactly. When electrons are placed in a par$cular quantum level, they prefer the orbitals in the order s, p, d, and then f. Copyright Cengage Learning. All rights reserved 37

38 Sec$on 7.9 Polyelectronic Atoms n=3 l = 2 n=3 l = 0 n=2 l = 0 n=3 l = 1 n=2 l = 1 n=1 l = 0 Copyright Cengage Learning. All rights reserved 38

39 Sec$on 7.10 The History of the Periodic Table Originally constructed to represent the paherns observed in the chemical proper$es of the elements. Mendeleev is given the most credit for the current version of the periodic table because he emphasized how useful the periodic table could be in predic$ng the existence and proper$es of s$ll unknown elements. Copyright Cengage Learning. All rights reserved 39

40 Sec$on 7.11 The AuIau Principle and the Periodic Table Aurau Principle As protons are added one by one to the nucleus to build up the elements, electrons are similarly added to hydrogen-like orbitals. An oxygen atom has an electron arrangement of two electrons in the 1s subshell, two electrons in the 2s subshell, and four electrons in the 2p subshell. Oxygen: 1s 2 2s 2 2p 4 Copyright Cengage Learning. All rights reserved 40

41 Sec$on Exercise 7.11 The AuIau Principle and the Periodic Table Fill up electrons in lowest energy orbitals (Aufbau principle) B 5 electrons B 1s 2 2s 2 2p 1 Li 3 electrons Li 1s 2 2s 1 He 2 electrons He 1s 2 H 1 electron H 1s 1 7.9

42 Sec$on 7.11 The AuIau Principle and the Periodic Table Hund s Rule The lowest energy configura$on for an atom is the one having the maximum number of unpaired electrons allowed by the Pauli principle in a par$cular set of degenerate (same energy) orbitals. Copyright Cengage Learning. All rights reserved 42

43 Sec$on 7.11 The AuIau Principle and the Periodic Table Orbital Diagram A nota$on that shows how many electrons an atom has in each of its occupied electron orbitals. Oxygen: 1s 2 2s 2 2p 4 Oxygen: 1s 2s 2p Copyright Cengage Learning. All rights reserved 43

44 Sec$on 7.11 The AuIau Principle and the Periodic Table Valence Electrons The electrons in the outermost principal quantum level of an atom. 1s 2 2s 2 2p 6 (valence electrons = 8) The elements in the same group on the periodic table have the same valence electron configura$on. Copyright Cengage Learning. All rights reserved 44

45 Sec$on 7.11 The AuIau Principle and the Periodic Table Order of orbitals (filling) in multi-electron atom 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s 7.7

46 Sec$on 7.11 The Orbitals AuIau Being Principle Filled for and Elements the Periodic in Various Table Parts of the Periodic Table Copyright Cengage Learning. All rights reserved 46

47 Sec$on 7.12 Periodic Trends in Atomic Proper,es Periodic Trends Ioniza$on Energy Electron Affinity Atomic Radius

48 Sec$on 7.12 Periodic Trends in Atomic Proper,es Ioniza$on Energy Energy required to remove an electron from a gaseous atom or ion. X(g) X + (g) + e Mg Mg + + e I 1 = 735 kj/mol (1 st IE) Mg + Mg 2+ + e I 2 = 1445 kj/mol (2 nd IE) Mg 2+ Mg 3+ + e I 3 = 7730 kj/mol *(3 rd IE) *Core electrons are bound much more $ghtly than valence electrons.

49 Sec$on 7.12 Periodic Trends in Atomic Proper,es Ioniza$on Energy In general, as we go across a period from lex to right, the first ioniza$on energy increases. Why? Electrons added in the same principal quantum level do not completely shield the increasing nuclear charge caused by the added protons. Electrons in the same principal quantum level are generally more strongly bound from lex to right on the periodic table.

50 Sec$on 7.12 Periodic Trends in Atomic Proper,es Ioniza$on Energy In general, as we go down a group from top to bohom, the first ioniza$on energy decreases. Why? The electrons being removed are, on average, farther from the nucleus.

51 Sec$on 7.12 Periodic Trends in Atomic Proper,es The Values of First Ioniza$on Energy for the Elements in the First Six Periods

52 Sec$on 7.12 Periodic Trends in Atomic Proper,es Successive Ioniza$on Energies (KJ per Mole) for the Elements in Period 3

53 Sec$on 7.12 Periodic Trends in Atomic Proper,es Electron Affinity Energy change associated with the addi$on of an electron to a gaseous atom. X(g) + e X (g) In general as we go across a period from lex to right, the electron affini$es become more nega$ve. In general electron affinity becomes more posi$ve in going down a group.

54 Sec$on 7.12 Periodic Trends in Atomic Proper,es Atomic Radius In general as we go across a period from lex to right, the atomic radius decreases. Effec$ve nuclear charge increases, therefore the valence electrons are drawn closer to the nucleus, decreasing the size of the atom. In general atomic radius increases in going down a group. Orbital sizes increase in successive principal quantum levels.

55 Sec$on 7.12 Periodic Trends in Atomic Proper,es Atomic Radii for Selected Atoms

56 Sec$on 7.13 The Proper,es of a Group: The Alkali Metals The Periodic Table Final Thoughts 1. It is the number and type of valence electrons that primarily determine an atom s chemistry. 2. Electron configura$ons can be determined from the organiza$on of the periodic table. 3. Certain groups in the periodic table have special names. Copyright Cengage Learning. All rights reserved 56

57 Sec$on 7.13 The Proper,es of a Group: The Alkali Metals Special Names for Groups in the Periodic Table Copyright Cengage Learning. All rights reserved 57

58 Sec$on 7.13 The Proper,es of a Group: The Alkali Metals The Periodic Table Final Thoughts 4. Basic division of the elements in the periodic table is into metals and nonmetals. Copyright Cengage Learning. All rights reserved 58

59 Sec$on 7.13 The Proper,es of a Group: The Alkali Metals Metals Versus Nonmetals Copyright Cengage Learning. All rights reserved 59

60 Sec$on 7.13 The Proper,es of a Group: The Alkali Metals The Alkali Metals Li, Na, K, Rb, Cs, and Fr Most chemically reac$ve of the metals Ø React with nonmetals to form ionic solids Going down group: Ø Ioniza$on energy decreases Ø Atomic radius increases Ø Density increases Ø Mel$ng and boiling points smoothly decrease Copyright Cengage Learning. All rights reserved 60