Quantium_theory,Models of the atoms._.pdf
- 1. MODELS OF THE ATOM Beginning with Rutherford
- 2. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC PROBLEMS WITH RUTHERFORD’S MODEL It didn’t explain WHY metals and metal compounds give off characteristic colors when they are flame tested It didn’t explain why metals glow when heated – first red, orange yellow and then white It didn’t explain the CHEMICAL properties of elements
- 3. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC BOHR’S THEORY Electrons are located at specific energy levels surrounding the nucleus Each rung on the ladder represents an energy level The higher the energy level – the farther it is from the nucleus Bohr thought the electrons moved in fixed ORBITS around the nucleus – we know this is not true today
- 4. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC BOHR MODEL First model of the electron structure Gives levels where an electron is most likely to be found Incorrect today, but a key in understanding the atom 4
- 5. Section 7.4 The Bohr Model Return to TOC Return to TOC 5 • Bohr’s model gave hydrogen atom energy levels consistent with the hydrogen emission spectrum. • Ground state – lowest possible energy state (n = 1) • Bohr’s model is incorrect. This model only works for hydrogen. • Electrons do not move around the nucleus in circular orbits. Electronic Transitions in the Bohr Model for the Hydrogen Atom a) An Energy-Level Diagram for Electronic Transitions Electronic Transitions in the Bohr Model for the Hydrogen Atom b) An Orbit- Transition Diagram, Which Accounts for the Experimental Spectrum
- 6. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC SCHRÖDINGER'S THEORY He agreed that electrons have a specific amount of energy He believed that the distance between rungs on the ladder were not consistent – they get closer together as you move higher up Quantum – the amount of energy needed to move from one energy level to another The electrons move in regions of probability around the nucleus called ORBITALS
- 7. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC Quantum theory, also called wave mechanics, describes the arrangement and space occupied by electrons. Orbitals refers to the three-dimensional regions in space where there is a high probability of finding an electron around an atom. 7
- 8. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC CHARACTERISTICS OF ELECTRONS ⚫ Extremely small mass ⚫ Located outside the nucleus ⚫ Moving at extremely high speeds in a sphere ⚫ Have specific energy levels 8
- 9. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC ENERGY OF ELECTRONS ⚫ When atoms are heated, bright lines appear called line spectra ⚫ Electrons in atoms arranged in discrete levels. ⚫ An electron absorbs energy to “jump” to a higher energy level. ⚫ When an electron falls to a lower energy level, energy is emitted. 9
- 10. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC LOSS AND GAIN OF ENERGY 10 G a I n L o s s
- 11. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC LEARNING CHECK Answer with 1) Energy absorbed 2) Energy emitted 3) No change in energy A. What energy change takes place when an electron in a hydrogen atom moves from the first (n=1) to the second shell (n=2)? B. What energy change takes place when the electron moves from the third shell to the second shell? 11
- 12. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC SOLUTION A. 1) Energy absorbed B. 2) Energy emitted 12
- 13. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC RELATIVE ORBITAL SIZE Difficult to define precisely. Orbital is a wave function. 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. 13 • We do not know the detailed pathway of an electron. •The electrons move in regions of probability around the nucleus called ORBITALS
- 14. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC THE ELECTRONS MOVE IN REGIONS OF PROBABILITY AROUND THE NUCLEUS CALLED ORBITALS DEFINING THESE ORBITALS: Quantum Numbers are used to define: The energy of the electron The electron’s relative distance from the nucleus The size and shape of the ORBITAL The pairings of the electrons
- 15. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC QUANTUM NUMBERS Principle Quantum Number (n) – define the energy of the electron n=1 is closest to the nucleus – low energy n=2 is farther than n=1, slightly more energy n=3 is farther than n=1 and n=2, still increasing in energy n=4 ….. Remember – The difference in energy between energy levels decreases as “n” increases
- 16. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC SUBLEVELS Within each principle energy level (n) – there are sublevel(s). The larger the value of ‘n’, the more sublevels you can have. Sublevels – named by their shape s – sphere p – pear d- dumbbell f - fundamental
- 17. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC TWO REPRESENTATIONS FOR AN S ORBITAL Figure 3.16, pg. 77 Investigating Chemistry, 2nd Edition © 2009 W.H. Freeman & Company
- 18. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC REPRESENTATIONS FOR P ORBITALS EACH ORBITAL CAN HOLD UP TO 2 ELECTRONS, REGARDLESS OF SHAPE. THIS SET OF THREE ORBITALS HOLDS 6 ELECTRONS. Figure 3.17, pg. 77 Investigating Chemistry, 2nd Edition © 2009 W.H. Freeman & Company
- 19. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC THERE IS A SET OF FIVE DIFFERENT D ORBITALS. THERE IS A SET OF SEVEN F ORBITALS. EACH ORBITAL REGARDLESS OF ITS SHAPE HOLDS 2 ELECTRONS.
- 20. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 20 1s Orbital
- 21. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 21 Two Representations of the Hydrogen 1s, 2s, and 3s Orbitals
- 22. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 22 2px Orbital
- 23. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 23 2py Orbital
- 24. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 24 2pz Orbital
- 25. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 25 The Boundary Surface Representations of All Three 2p Orbitals
- 26. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 26 3dx2 -y2 Orbital
- 27. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 27 3dxy Orbital
- 28. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 28 3dxz Orbital
- 29. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 29 3dyz Orbital
- 30. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 30 Orbital 2 3 z d
- 31. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 31 The Boundary Surfaces of All of the 3d Orbitals
- 32. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 32 Representation of the 4f Orbitals in Terms of Their Boundary Surfaces
- 33. Section 7.5 The Quantum Mechanical Model of the Atom Return to TOC Return to TOC SUBLEVELS Principle Energy Level Sublevel n= 1 s n=2 s and p n=3 s and p and d n=4 s, p, d, and f NOTICE: The value of ‘n’ tells you how many sublevels are present in that energy level
- 34. Section 7.6 Quantum Numbers Return to TOC Return to TOC 34 • Principal quantum number (n) – size and energy of the orbital. • Angular momentum quantum number (l) – shape of atomic orbitals (sometimes called a subshell). • Magnetic quantum number (ml) – orientation of the orbital in space relative to the other orbitals in the atom.
- 35. QUANTUM NUMBERS FOR THE FIRST FOUR LEVELS OF ORBITALS IN THE HYDROGEN ATOM 35
- 36. Section 7.6 Quantum Numbers Return to TOC Return to TOC 36 Exercise For principal quantum level n = 3, determine the number of allowed subshells (different values of l), and give the designation of each. (hint refer to previous chart) # of allowed subshells = 3 l = 0, 3s l = 1, 3p l = 2, 3d
- 37. Section 7.6 Quantum Numbers Return to TOC Return to TOC 37 Exercise For l = 2, determine the magnetic quantum numbers (ml) and the number of orbitals. (note refer to previous chart) magnetic quantum numbers = –2, – 1, 0, 1, 2 number of orbitals = 5
- 38. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC Locating these on the Periodic Table Principle Energy Level (n) – is the period in the periodic table The Sublevels are located in specific regions – Color these together
- 39. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 39 • The periodic table is structured so that elements with the same type of valence electron configuration are arranged in columns. • The left-most columns include the alkali metals and the alkaline earth metals. In these elements the valence s orbitals are being filled • On the right hand side, the right-most block of six elements are those in which the valence p orbitals are being filled • In the middle is a block of ten columns that contain transition metals. These are elements in which d orbitals are being filled • Below this group are two rows with 14 columns. These are commonly referred to the f-block metals. In these columns the f orbitals are being filled
- 40. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC 40 • The periodic table is structured so that elements with the same type of valence electron configuration are arranged in columns. Important facts to remember: • 2, 6, 10 and 14 are the number of electrons that can fill the s, p, d and f subshells (the l=0,1,2,3 azimuthal quantum number) • The 1s subshell is the first s subshell, the 2p is the first p subshell • 3d is the first d subshell, and the 4f is the first f subshell
- 41. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC Naming the sublevels 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f
- 42. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC Orbitals Orbitals are regions of probability – each orbital can hold a maximum of 2 e- The ‘s’ sublevel has 1 orbital The ‘p’ sublevel has 3 orbitals The ‘d’ sublevel has 5 orbitals The ‘f’ sublevel has 7 orbitals
- 43. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC Orbitals Do you have to memorize this? NO Look at the sublevel regions that you colored in on your periodic table.
- 44. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC Orbitals Count how many electrons are in the ‘s’ sublevel 2 This means that since there are two electrons, and each orbital can hold two electrons, that there is only ONE orbital.
- 45. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC Orbitals Count how many electrons are in the ‘p’ sublevel 6 This means that since there are six electrons, and each orbital can hold two electrons, that there are THREE orbitals.
- 46. Section 7.7 Orbital Shapes and Energies Return to TOC Return to TOC Orbitals Count how many electrons are in the ‘d’ sublevel 10 This means that since there are ten electrons, and each orbital can hold two electrons, that there are FIVE orbitals.
- 47. ORBITALS Count how many electrons are in the ‘f’ sublevel 14 This means that since there are fourteen electrons, and each orbital can hold two electrons, that there are SEVEN orbitals.