Unit 5 Electrons in Atoms

1. Unit 5Electrons in Atoms Chemistry I Mr. Patel SWHS

2. Topic Outline • Continue Learning Major Ions • Atomic Models (5.1) • Electron Configurations (5.2) • Light and Quantum Mechanics (5.3) • Lewis Dot Structures (7.1)

3. Atomic Models • Democritus’s Model • Thomson’s Plum Pudding Model • Rutherford’s Model • Electrons travel in orbit around nucleus • Could NOT explain chemical properties of elements • Need a model for electrons

4. Bohr Model • Niels Bohr – electrons is found in a specific orbit around nucleus • Each orbit has a specific energy = energy level • The further away from the nucleus, the higher the energy

5. Bohr Model

6. Bohr Model • An electron can move between levels • Can not be between levels • Think of a ladder • An electron must gain or lose energy to change levels • A quantum of energy – energy to move to another level

7. Bohr Model • More energy between levels when closer to nucleus • Less energy between levels when farther • Energy levels get closertogether

8. Bohr Model • Ground state – lowest energy state for an electron • Excited state – any higher energy state

10. Electron Excitation http://www.youtube.com/watch?v=4jyfi28i928&feature=relmfu

11. Bohr Model • Each ring on a Bohr Model is labeled as “n” • n must be a whole number • n=1, n=2, n=3, etc. (period number) • Each ring (n) can hold a specific number of electrons • n=1 2 electrons • n=2 8 electrons • n=3 18 electrons • n=4 32 electrons

13. Drawing Bohr (Rutherford) Diagrams http://www.youtube.com/watch?v=sKAzHE7A7rQ&feature=relmfu

14. Ex: Draw the Bohr Diagram for Hydrogen.

15. Ex: Draw the Bohr Diagram for Neon.

16. Ex: Draw the PEL Diagram for Bromine.

17. Bohr Model • Correct: Electrons have energy levels and can move • Incorrect: Electrons move in orbits • Matter has a Wave-Particle Duality

18. Dual Nature of Electrons Electrons as Particles Electrons as Waves Young's Double Slit Experiment PhotoelectricEffect

19. Modern Theory • Rutherford and Bohr based models on behavior of large objects • Small objects behave differently – quantum mechanics • Schrödinger Equation solutions  quantum mechanical model of the atom

20. Schrödinger Equation

21. The Cat – A Thought Experiment • Schrodinger Cat 1 • Schrodinger Cat 2

22. Quantum Mechanical Model • Determines the allowed energies of the electrons • The probability of where an electron is – electrons housed in electron clouds

23. Atomic Orbitals • Region in space where there is a high probability of finding an electron • Principal quantum number (n) – energy level • think of the ring labels of the Bohr model • Each energy level can be made up of sublevels – orbitals of similar energy but different shapes

24. 1. s orbital • Shape: sphere

25. 2. p orbital • Shape: Dumbbell

26. 3. d orbital • Shape: clover (mostly)

27. 4. f orbital • Shape: multiple clover

28. Atomic Orbitals http://www.youtube.com/watch?v=K-jNgq16jEY

29. Electron Configurations • Electrons found in orbitals • Electron configuration – ways in which various electrons are arranged in orbitals • 4 orbitals: s (2 electrons), p (6 electrons) d (10 electrons), f (14 electrons)

30. Three Rules to find Elec. Config • Aufbau Principle • Electrons occupy orbitals of lower energy first • For same n, low to high energy: s, p, d, f

31. Three Rules to find Elec. Config • Pauli Exclusion Principle • Each atomic orbital can have at most 2 electron • Each electron in an orbital must have opposite spins • 2 spins: spin up or spin down • How we draw: 1 electron in s orbital: ____ 2 electrons in s orbital: ____ • We use arrow with “half head”

32. Three Rules to find Elec. Config • Hund’s Rule • Electrons occupy orbitals to maximize spin • For same n, place electrons spin up first then pair them with spin down • 1 electron in p orbital ____ ____ ____ • 2 electrons in p orbital ____ ____ ____ • 3 electrons in p orbital ____ ____ ____ • 4 electrons in p orbital ____ ____ ____ • 5 electrons in p orbital ____ ____ ____ • 6 electrons in p orbital ____ ____ ____

33. Orbital Blocks on PT • s-block: Groups 1A and 2A (exception: He) • p-block: Groups 3A-8A (exception: He) • d-block: transition metals • f-block: inner transition metals • Remember, the period number is n = principal energy level

34. Orbital Blocks on PT

35. How to write electron configuration • Ex: What is the electron configuration for O? • O = oxygen, atomic number 8 = 8 electrons • Draw spaces: ____ ____ ____ ____ ____ 1s 2s 2p • Fill spaces according to rules: ____ ____ ____ ____ ____ 1s 2s 2p • Write: 1s22s22p4

36. How to write electron configuration • Ex: What is the electron configuration for C? • C = carbon, atomic number 6 = 6 electrons • Draw spaces: ____ ____ ____ ____ ____ 1s 2s 2p • Fill spaces according to rules: ____ ____ ____ ____ ____ 1s 2s 2p • Write: 1s22s22p2

37. 3 ways to write electron configurations • Using boxes and arrows ____ ____ ____ ____ ____ 1s 2s 2p • Long EC: Cl: 1s22s22p63s23p5 • Short EC: Cl: [Ne] 3s23p5 • Put last noble gas in brackets and write electrons from there

38. Writing EC • This is much easier than it looks. • Simply, start at hydrogen and walk to the desired element counting all the elements you pass

39. Ex. Write EC (all three ways) for Boron.

40. Ex. Write EC (all three ways) for Mg.

41. Ex. Write EC (all three ways) for V.

42. Ex. Write EC (long and short) for Fr.

43. A Look Back… • So far we have covered (and mastered): • Evolution of the Atomic Model • Democritus, Thomson, Rutherford, Bohr, QM • Bohr Model and Bohr Diagram • Quantum Mechanical Model and Orbitals • Rules of Electron Configuration • Writing Electron Configurations

44. Electrons • Chemical reactions are the breaking and forming of bonds • There are two types of bonds: covalent and ionic (and metallic) = next unit • Bonding involves the movement of electrons

45. Valence Electrons • Valence Electron: electrons in the highest occupied level • These are the electrons that participate in bonding!!!

46. Valence Electrons • You do not have to draw a Bohr Model every time you need to determine the VE’s • The valence electrons (valency) for an atom is the same as the group number • Note: In general, transition metals have two valence electrons.

47. Determine the valence electrons for: • Ca • Be • O • Si • H • Ne • Ar • 2 • 2 • 6 • 4 • 1 • 10 • 10

48. Lewis Dot Structures • Show bonding electrons • These structures show only valence electrons. • How to draw: • Write Symbol for element • Determine group number • Place that many (group number) dots around symbol N B

49. Lewis Dot Structures 1 2 3 4 5 6 7 8

50. Lewis Structures (Future)