1. Unit 5: Atomic Structure
Trimble
CDO CP Chemistry

2. Dalton’s Atomic Theory
1803 – John Dalton linked the existence of elements, which cannot be decomposed chemically, to the idea of atoms, which are indivisible.

3. Postulates
All matter is made of atoms. These indivisible and indestructible objects are the ultimate chemical particles.
Atoms cannot be created or destroyed
Atoms of the same element are alike in every way

4. Postulates cont. Atoms of different elements are different
Atoms can combine together in small numbers to form molecules (compounds)

5. Basic Components of the Atom
There are 3 fundamental subatomic particles
electron relative mass = amu relative charge = -1
proton relative mass = 1 amu
relative charge = +1
neutron relative mass = 1 amu
charge = 0

6. Atomic Structure
Nucleus is found at the center of the atom. Contains the protons and neutrons.
The number of protons in the nucleus determines what element an atom is.

7. Electrons are found in the space around the nucleus.
Atomic Structure
Electrons are found in the space around the nucleus.

8. Electrically Neutral Atoms
For any neutral atom, the number of negatively charged electrons around the nucleus equals the number of positively charged protons in the nucleus

9. Important Note
To chemists the electrons are the most important part of the atom, because they are the first part of the atom that contacts another atom.

10. Isotopes

11. All atoms of the same element have the same number of protons.
Atomic Number
All atoms of the same element have the same number of protons.
This number is called the atomic number and is given the symbol Z.
The atomic number is the whole number in each element box on the periodic table.

12. This number is not listed on the periodic table
Mass Number
The sum of the number of protons and neutrons in an atom is called the mass number and is represented with the symbol A.
This number is not listed on the periodic table

13. Atoms having the same atomic number Z but a different mass number A.
Isotopes
Atoms having the same atomic number Z but a different mass number A.
Isotopes are atoms of the same element, but they have different masses because they have different numbers of neutrons.

14. Nuclear Symbol of an Atom

15. Hyphen Notation
Hyphen notation reports the element name, then the mass number of the isotope after a dash.
Helium-4

16. Example: Counting Sub Atomic Particle Isotopes
How many protons and electrons are in found in each of the following neutral elements: Li P Ag Xe U

17. Example: Counting Sub Atomic Particle Isotopes
Determine the number of protons, electrons, and neutrons in each of the following:

18. Oxygen-18 Calcium-40 Lead-204 Mercury-196
Example: Counting Sub Atomic Particle Isotopes
Determine the number of protons, electrons, and neutrons in each of the following:
Oxygen-18
Calcium-40
Lead-204
Mercury-196

19. Example: Counting Sub Atomic Particle Isotopes
Write the nuclear symbol and hyphen notation name for each of the following elements:
7 protons, 7 electrons, 8 neutrons
28 protons, 28 electrons, 30 neutrons
47 protons, 47 electrons, 62 neutrons
50 protons, 50 electrons, 64 neutron

20. Ions

21. Ion Formation
Atoms can gain or lose electrons to form ions
Cation – an atom that has lost an electron and forms a positive charge
Anion – an atom that has gained an electron and is negatively charged

22. Ionic Symbols
Ions are indicated by writing the element symbol with charge value written in the upper right hand corner
The number one is never written
Na+
O2-

23. Ion Formation
To determine the charge on an ion subtract the number electrons from the number of protons Charge = protons - electrons

24. Example: Counting Sub Atomic Particle - Ions
Give the number of protons and electrons in the following:
Li+
Al3+
N3-
Pb4+
Br-

25. 17 protons, 18 electrons 38 protons, 36 electrons
Example: Counting Sub Atomic Particle - Ions
Write the ionic symbol for each of the following ions.
17 protons, 18 electrons
38 protons, 36 electrons
16 protons, 18 electrons
31 protons, 28 electrons

26. Example: Counting Sub Atomic Particle - Ions
Determine the number of protons, electrons, and neutrons in the following:

27. 15 protons, 18 electrons, 17 neutrons
Example: Counting Sub Atomic Particle - Ions
Write the nuclear symbol, with charge is needed, for the following:
15 protons, 18 electrons, 17 neutrons
12 protons, 10 electrons, 14 neutrons
16 protons, 16 electrons, 20 neutrons
35 protons, 36 electrons, 46 neutrons

28. Average Atomic Mass

29. Average Atomic Mass
The weighted average of the naturally occurring isotopes of an element.
Found by averaging the natural abundances of its isotopes

30. Calculating Average Atomic Mass (amu)
To calculate the average atomic mass multiply the percent abundance of an isotope by its mass or mass number.
Do this for each isotope and then add the results together

31. Average Atomic Mass
Rubidium has two common isotopes, Rb-85 and Rb-87. If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium?

32. Uranium has three common isotopes. If the abundance of 234U is
Uranium has three common isotopes. If the abundance of 234U is .01%, the abundance of 235U is .71%, and the abundance of 238U is 99.28%, what is the average atomic mass of uranium?

33. Calculating Atomic Masses
For boron, 19.9% occurs as 10B and 80.1% occurs as 11B. The isotopic mass of 10B is and 11B is

34. Practice
Gallium consists of two isotopes: Ga-69 with a mass of amu accounts for 60.11% and Ga-71 with a mass of amu accounts for the rest. What is the average mass of gallium?

35. Electron Arrangement

36. Electromagnetic spectrum
Electromagnetic radiation – comes in differing forms
All EMR travels at the same speed (c) but can be distinguished by their different wavelengths (l)

37. Electromagnetic Radiation

38. Visible Spectrum

39. Purple – 400 nm Blue – 475 nm Green – 510 nm Yellow – 570 nm
Wavelengths of Visible Spectrum
Purple – 400 nm
Blue – 475 nm
Green – 510 nm
Yellow – 570 nm
Orange – 590 nm
Red – 650 nm

40. Electromagnetic spectrum
Frequency (f) – the number of waves which pass through a particular point.
Measured in Hertz (Hz), which is equal to 1/s.
Wavelength (l) - the distance between crests in a wave.
The shorter the l the higher the frequency (f)

41. Calculating Wavelength or Frequency
c = f l
C = 3.0 x 108 m/s

42. Practice
The distinctive green color of Aurora Borealis is caused by the interaction of the radiation with oxygen and has a frequency of 5.38 x Hz. What is the wavelength of this light?

43. Light with a frequency of 7
Light with a frequency of 7.26 x 1014 Hz lies in the violet region of the visible spectrum. What is the wavelength of this frequency of light?

44. A certain violet light has a wavelength of 413 nm
A certain violet light has a wavelength of 413 nm. What is the frequency of this light?

45. Energy of Light
The energy of light can be calculated using the following equation
E = hf
E = energy of light in Joules (J)
h = Planck’s constant = x 10-34
f = frequency

46. Energy of Light
Calculate the energy of a photon of radiation with a frequency of 8.5 x 1014 Hz.

47. Calculate the energy of a photon of radiation with a wavelength of 6
Calculate the energy of a photon of radiation with a wavelength of 6.4 x 10-7 m.

48. Calculate the energy of a photon of radiation with a wavelength of 6
Calculate the energy of a photon of radiation with a wavelength of 6.4 x 10-7 m.

49. What is the energy of light whose wavelength is 4.06 x 10-11 m?

50. Electron Configuration

51. Orbital Diagram An orbital is a potential space for an electron.
Orbitals are represented by boxes or lines grouped by sublevel with small arrows indicating the electrons.

52. Pauli Exclusion Principle
An atomic orbital can hold a maximum of 2 electrons and those 2 electrons must have opposite spins.
An electron is represented by an arrow.
Spin is represented by the arrow facing up or down.

53. Aufbau Principle Electrons are placed in the lowest energy
level first.
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p

54. Hund’s Rule
When filling sublevels other than s, electrons are placed in individual orbitals first, before they are paired up.
They must be placed singly before doubly.

55. Sublevels The “s” sublevel can hold 2 electrons.
The “p” sublevel can hold 6 electrons.
2 electrons in each of the 3 orbitals (x, y, z)
The “d” sublevel can hold 10 electrons.
2 electrons in each of the 5 orbitals.
The “f” sublevel can hold 14 electrons.
2 electrons in each of the 7 orbitals.

56. Practice Problems
Write the orbital diagram for Fluorine.

57. Practice Problems
Write the orbital diagram for Magnesium.

58. Electron Configuration
Shows the arrangement of electrons in an atom.

59. Electron Configuration
The rules for electron configurations is the same as orbital diagrams
However…
Instead of drawing in orbitals and arrows, write the number of electrons in the sublevel in superscript after the sub level name.

60. Practice Problems
Write the electron configuration and the orbital diagram for Sulfur.

61. Practice Problems
Write the electron configuration and the orbital diagram for Potassium.

62. Organization of Orbitals
The periodic table has organized the orbitals.
The “s”
orbitals
The “p”
The “d”
The “f” orbitals

63. Organization of Orbitals
The first row is Principal Energy Level 1.
The second row is Principal Energy Level 2.
Principal
Energy Level
3 begins in
the 3rd row.
Energy Level 4 begins
in the 4th row.

64. and so the pattern continues…

65. Noble Gas Configuration
Is an abbreviated version of electron configuration.
Uses the noble gas that precedes the element, then the electron configuration that comes after the noble gas.
Used for elements with larger atomic numbers.
Example:
Nitrogen

66. Noble Gas Configuration
Is important because it shows the valence electrons present in an atom.
Nitrogen has an atomic number of 7. It has 7 total electrons. If you look at the electron configuration, you can count 7 electrons.

67. Noble Gas Configuration
But if you look at the Noble Gas Configuration, you can count 5 electrons.
These 5 electrons are the valence electrons, the electrons found in the outermost energy level. These are the electrons available for bonding.

68. Valence Electrons The periodic table organizes valence electrons.
The number
of valence
electrons
are written
above each
column in
the diagram.

69. Practice Problems
Write the noble gas configuration and the orbital diagram for Iron.

70. Practice Problems
Write the noble gas configuration and the orbital diagram for Tin.

71. IONIZATION ENERGY
Ionization energy, Ei: minimum energy required to remove an electron from the ground state of an atom in the gas phase. M(g) + h  M+ + e.
Ei related to electron arrangement
Sign of the ionization energy is always positive.

72. Ionization Energy: Periodic Table
Ionization Energy vs atomic #

73. Successive Ionization Energies
Atoms can lose more than one electron
Each electron lost requires more energy than the one before it
Electrons removed from levels closer to the nucleus requires more energy

74. Ionization Energy of Aluminum