1. Chapter 5
Electrons in Atoms

2. 5.1 Light and Quantized Energy
Light, a form of electromagnetic radiation has characteristics of both waves and particles.

3. The Wave Nature of Light
Light is a type of electromagnetic radiation
Form of energy that exhibits wavelike behavior as it travels through space

4. Characteristics of waves
Wavelength (λ): Shortest distance between equivalent points on a wave
Amplitude: - waves height from origin to crest or origin to trough

5. Frequency (ν): number of waves that pass a given point per second
SI unit = hertz (Hz)

6. All electromagnetic waves, including light travel at 3
All electromagnetic waves, including light travel at 3.00 x 108 m/s (c)
c = λν

7. Electromagnetic spectrum
Visible light is only a very small part of the electromagnetic spectrum
EM spectrum includes all forms of electromagnetic radiation
Differences between types of radiation = frequency & wavelength

9. What is the wavelength of a microwave that has a frequency of 3
What is the wavelength of a microwave that has a frequency of 3.44 x 109 Hz?
Light reflected from a green leaf has a wavelength of 4.90 x m. What is the frequency of the light?

10. The Particle Nature of Light
Wave model of light cannot explain all the ways light interacts with matter
Metal glows when heated
Iron = grey at room temp, then glows red, then orange, the blue

11. The quantum concept
Matter can gain or lose energy only in small, specific amounts called quanta
Stairs
Quantum = minimum amount of energy that can be gained or lost by an atom

12. Energy of a quantum = Planck’s constant x frequency
Planck’s constant = x J*s
Equantum = hν

13. The photoelectric effect
Electrons are emitted from a metal’s surface when light at or above a certain frequency shines on the surface

14. Light = beam of bundles of energy (photons)
Einstein proposed the dual nature of light (wave-like & particle- like) to explain the photoelectric effect
Light = beam of bundles of energy (photons)
Photons = massless particles that carry a quantum of energy

15. E photon = hv
Every object gets its color by reflecting a certain portion of visible light. The color is determined by the energy of the reflected photons. What is the energy of a photon from violet light if it has a frequency of x 1014 Hz

16. The blue color in fireworks has a wavelength of 4. 5 x 10-10 m
The blue color in fireworks has a wavelength of 4.5 x m. How much energy does one photon of this light carry?

19. Atomic Emission Spectra
Set of frequencies of the electromagnetic waves emitted by atoms of the element
Found by putting gas into tube and charging it.
Light viewed through prism & colors separate
Each line of color = photon with specific energy

21. Each element’s emission spectrum is unique and can be used to identify the element.

22. 5.2 Quantum Theory and the Atom
Electrons behave much like a person climbing a ladder

23. Bohr’s Model of the Atom
Proposed atoms only have certain allowable energy states
Ground state – lowest allowable energy state for an atom
Excited state – an atom that has gained energy

24. Electrons move around nucleus in circular orbits (energy levels)
Orbits closest to nucleus have lowest energy

25. Bohr assigned a number, n, to each orbit (quantum number)
Orbit closest to nucleus = energy level 1 & n = 1

26. Quantum theory & emission spectra
When electrons are excited the move to higher energy levels
Electron drops from higher to lower energy level and emits a photon corresponding to the energy difference between the two levels
Photon = color of light shown

29. Limits of Bohr Model Only explains Hydrogen’s emission spectrum
Does not account for chemical behavior of atoms
Electrons do NOT move around nucleus in circular orbits

30. Quantum Mechanical Model
Louis de Broglie – proposed electrons can have wave characteristics
Werner Heisenberg – it is impossible to know the exact position of an electron at any time (Heisenberg uncertainty principle)

31. The act of seeing an electron changes its path!

32. The only thing that can be known about an electron is the probability for it to occupy a certain region around the nucleus
Schrodinger – treated electrons like waves & developed the quantum mechanical model of the atom

33. Atomic orbital – 3D region around the nucleus which describes an electrons probable location
More dense areas = more likely to find electron

34. Atomic Orbitals Bohr’s quantum numbers are now called energy levels
Principal energy level – the major energy levels of an atom
Lowest energy level n = 1
n values range 1 – 7

35. Energy Sublevels
Smaller levels within energy levels where electrons can move (s, p, d, f)
n = 1 : 1 sublevel
n = 2 : 2 sublevels
n = 3 : 3 sublevels
n = 4 – 7 : 4 sublevels

36. Sublevels are made of orbitals
Each type of sublevel has a different number and shape of orbitals
2 electrons can fit in each orbital

37. S sublevel = 1 orbital
p sublevel = 3 orbitals
d sublevel = 5 orbitals
f sublevel = 7 orbitals
Each orbital can be filled: (2 e-), half filled: (1 e-), or empty: (0 e-)

38. Shapes of sublevels S = sphere (1 orbital)
p = peanut shell (3 orbitals)
d = clover leaf (5 orbitals)
f = shapes vary (7 orbitals)

40. Energy Levels, Sublevels & Orbitals
Energy level 1 = closest to nucleus
One sublevel = s
One orbital = 1s
Energy level 2
2 sublevels = s and p
4 orbitals = 2s, 2px, 2py, 2pz

41. Higher energy levels have all four sublevels
Three sublevels = s, p, and d
Nine orbitals = 3s, 3px, 3py, 3pz, five 3d orbitals
Energy level 4
Four sublevels = s, p, d, and f
16 orbitals
Higher energy levels have all four sublevels

42. Catholic Central as an atom
Pretend you are an electron
Floor =
Classroom =
Desks =

43. 5.3 Electron Configurations
Electron configuration = the arrangement of electrons in an atom
Most stable, lowest energy configuration = ground state electron configuration

44. Which sublevels are in each energy level?
How many orbitals are in each sublevel?
How many electrons can each orbital hold?

45. The Aufbau Principle
The lowest energy levels are filled with electrons first

46. The Pauli Exclusion Principle
Only two electrons can occupy an orbital
The electrons must have opposite spins

47. Hund’s Rule
When electrons occupy orbitals of equal energy, one electron enters each orbital until all orbitals contain one electron with spins parallel

49. Draw the orbital diagram for the following atomsLi O Cl

50. Important questions using a Cl atom
Highest full energy level?
Highest full sublevel?
Highest occupied energy level?
Number of unpaired electrons?
Number of empty orbitals?

51. Electron configurations from orbital diagramsNa P Ar

52. Electron Configurations Beyond Row 3
Energy levels 3 and up overlap
4s is lower energy than 3d so it comes first!
Follow your diagonal diagram

54. What are the electron configurations of the following?Kr Ba

55. Abbreviated electron configurations
Elements in column 8A are noble gasses
All very stable and unreactive
All except He have 8 valence electrons
Ne: 1s22s22p6
Kr: 1s22s22p63s23p64s23d104p6

56. Noble gas configurations = base Ex: Ca
Ar:
Ca:
Ca abbreviated:

57. How to write abbreviated configurations
Find the noble gas in the row above the given element
Write its symbol in brackets
Add electrons into proper orbitals until total number of electrons is reached
Make sure you start after brackets with correct orbital!

58. Fr Pt As

59. EXCEPTIONAL ELECTRON CONFIGURATIONS
Up to atom number 23 there are no exceptions!
After that exceptions may occur in transition metals
Partially full orbitals are more stable that empty orbitals
Electrons will sometimes move to fill empty orbitals.

60. EX: Mo
[Kr]5s24d 4
[Kr]5s14d 5
Which version of molybdenum is more stable?
Would Zr be an exception?

61. Valence Electrons Electrons in the outermost s & p
Determine an atom’s properties

62. Boron: 1s22s22p1 Scandium: 1s22s22p63s23p64s23d1 Highest energy level
Valence electrons
Scandium: 1s22s22p63s23p64s23d1
Valence Electrons

63. Electron Dot Structures
Valence electrons are the only ones that are involved in chemical reactions
Dot structures show the valence electrons

64. How to draw a dot structure
Figure out how many valence electrons element has
Write the element symbol
Add dots to top, right, bottom, and left of symbol one at a time until all valence electrons are used
Remember: each orbital can only hold 2 dots

65. Phosphorus Bromine Oxygen Element Electron Configuration # of VE
Dot Diagram
Phosphorus
Bromine
Oxygen