The ATOM
Early Studies of the Atom
Daltons Atomic Theory
1803
* ALL ELEMENTS ARE COMPOSED ON INDIVISIBLE ATOMS
* ALL ATOMS OF A GIVEN ELEMENT ARE IDENTICAL
* ATOMS OF DIFFERENT ELEMENTS ARE DIFFERENT, WITH DIFFERENT MASSES
* COMPOUNDS ARE FORMED BY THE COMBINATION OF ATOMS OF DIFFERENT ELEMENTS
Structure of the Atom
J.J. Thomson
(1897) and the invention of the CATHODE RAY tube.
Electrons
Size: VERY SMALL charge: NEGATIVE
“plum pudding model” (draw below)

Description MASS OF THE REST OF THE ATOM WAS EVENLY DISTRIBUTED AND POSITIVELY
CHARGED, TAKING UP ALL THE SPACE NOT OCCUPIED BY ELECTRONS https://www.youtube.com/watch?v=dehxVQAUqBs
Ernest Rutherford
(1909) and the GOLD FOIL experiment.
Neutrons
Size: SMALL charge: NO CHARGE

Alpha particles: POSITIVELY charged particles.
“The Gold foil experiment” (draw and label experimental set-up below)
Description MOST OF THE PARTICLES PASSED THROUGH THE FOIL, SOME ALPHA PARTICLES
BOUNCED BACK
“The Gold foil experiment” (draw and label experimental the deflecting alpha particles below)

Description DEFLECTION OF THE APLHA PARTICLES SHOWED THAT ATOMS HAVE A DENSE,
POSITIVELY CHARGED CENTER.
Ernest Rutherford
(1909) and “The Gold foil experiment” CONCLUSION:

Atoms have a dense central core = NUCLEUS

The Nucleus is POSITIVELY charged.

Most of the atom is EMPTY space.
Protons
Size: SMALL charge: POSITIVE
Neutrons
Size: SMALL charge: NO CHARGE https://www.youtube.com/watch?v=FfY4R5mkMY8 https://www.youtube.com/watch?v=4z46Bs3fRCY
Modern Atomic Theory
Neils Bohr
(1913) and the “ PLANETARY” model.
“Planetary model” (draw below)

Description A CENTER NUCLEUS AND RINGS OF ORBITING ELECTRONS https://www.youtube.com/watch?v=q8N3dnx-5PE
Contains a center, a NUCLEUS , and rings of orbiting ELECTRONS.
Orbits are called concentric circles or SHELLS.
Outermost electrons are called “ VALENCE ” electrons.
Noble gases have a FULL valence shell. ( 8 ELECTRONS)
Maximum number of electrons that can fil an orbital are:
Shell 1: 2 electrons
Shell 2: 8 electrons
Electron structure can be found on the PERIODIC TABLE (reference table)
The Wave- Mechanical Model
, present day
“wave-mechanical model” (draw below) https://www.
youtube .com/watch?v=1bpG1lEjJfY
Description ENERGY IS VIEWED AS WAVES AND MATTER AS PARTICLES, WITH A DENSE
NUCLEUS
DEFINITION of an orbital: REGION IN WHICH AN ELECTRON OF A PARTICULAR AMOUNT OF
ENERGY IS MOST LIKELY TO BE LOCATED

Comprehensive history of the atom www.youtube.com/watch?v=-4Us5PTb4J8
Questions:
1.
1
2.
3
3.
1
4.
4
5. 2
6. 2
7. 1
8. 3
9.3
10. plum pudding model had electrons and protons mixed throughout the atom, the
planetary model has electrons in orbits with protons in the center nucleus.
11. Rutherford expect they would travel through the foil but some were deflected- the atom
had a dense core called a nucleus.
12. Rutherford- electron are infixed orbits, wave-mechanical model- electrons have both
wave and particle properties “cloud” not orbits
Subatomic Particles
Protons
Mass: 1 AMU charge: POSITIVE location : NUCLEUS
Neutrons
Mass: : 1 AMU charge: NO CHARGE location :NUCLEUS
Electrons
Mass:
1/1836 OF A PROTON
charge: NEGATIVE location :
ORBITAL/PRINCIPAL ENERGY LEVEL
Symbols:
ATOMIC NUMBER : represents the number of protons in the nucleus.

MASS NUMBER : sum of all the protons and neutrons in the nucleus.
Define isotope: ATOMS OF THE SAME ELEMENT THAT HAVE DIFFERENT NUMBERS OF
NEUTRONS, THEY HAVE DIFFERENT MASS NUMBERS BUT SAME ATOMIC NUMBER
Example: 1 H 2 H 3 H * all isotopes of hydrogen
1 1 1
Some symbols of isotopes
C-14 14 C
Carbon-14 14 C
6
* The number 14 always represents the MASS NUMBER
Sample problem #1: finding the number of neutrons in an atom.
FIND THE NUMBER OF NEUTRONS IN AN ATOM OF 79 Se ?
34
ATOMIC NUMBER = 34
MASS NUMBER= 79
NUMBER OF NEUTRONS= ?
NEUTRON= MASS NUMBER – ATOMIC NUMBER
NEUTRONS= 79-34
NEUTRONS = 45

Sample problem #2: calculating average atomic mass.
CARBON -12 = 98.89 %
Carbon -13 = 1.108%
12 amu X 0.9889= 11.87 amu
13 amu X 0.01108 = 0.1440 amu
11.87amu + 0.1440 amu= 12.01 amu
12.01 amu = Average atomic mass of all naturally occurring isotopes of Carbon
Location of electrons
Electrons
Mass:
1/1836 OF A PROTON
charge: NEGATIVE location :
ORBITAL/PRINCIPAL ENERGY LEVEL
Orbitals are called concentric circles or SHELLS OR PRINCIPAL ENERGY LEVELS.
Outermost electrons are called “ VALENCE” electrons.
Noble gases have a FULL valence shell. “ OCTET RULE”
Maximum number of electrons that can filL an orbital are:
Shell 1: 2 electrons
Shell 2: 8 electrons
GROUND STATE Electron structure can be found on the PERIODIC TABLE (reference table)
Electrons in the lowest available orbitals are said to be in the GROUND STATE.
Electrons that absorb energy and temporarily move to higher energy levels are said to be in the EXCITED STATE.

When an electron quickly returns to a ground state energy level it emits light.
Visible light produced by electrons is confined to narrow lines of color called the BRIGHT-LINE spectra.
Questions
13. 3
14. 3
15. 1
16. 3
17. 4
18. 4
19. 2
20. 4
22.1
23. 1
24. 3
25. 3
26. 2
27. 2
21. 2 28. 3
Electron Arrangement
Quantum theory was developed to explain the chemical behavior of atoms
The principal QUANTUM NUMBER describes the major energy level of an electron.
(PEL- 1,2,3,4, etc.)
Each energy level has one or more SUBLEVELS associated with it. (s,p,d,f)
Quantum numbers describe the distribution of electrons in an atom. The distribution of electrons is called the ELECTRON CONFIGURATION.
Found on the Periodic Table of Elements.
Writing electron configurations- follow the rules:
1.
EACH ADDED ELECTRON IS PLACED INTO A SUBLEVEL OF LOWEST AVAILABLE ENERGY.
2.
NO MORE THAN TWO ELECTRONS CAN BE PLACED INTO ANY ORIBITAL.
3.
A SINGLE ELECTRON MUST BE PLACED INTO EACH ORBITAL OF A GIVEN SUBLEVEL
BEFORE PAIRING TAKES PLACE
4.
OUTERMOST PRINCIPAL ENERGY LEVELS CAN ONLY CERTAIIN ELECTRONS IN s AND p
ORBITALS

Two methods for showing orbital notation
Method 1 Method 2
Questions
29. 3 36. 2
30. 1
31. 3
32. 4
37. 1
38. 1
39. 4
33. 4
34. 4
35. 1
40. 1
41.2
42. 3
43. 2
44. 4
45. 4
46. 3
47. 3
48. 4
49. 2
50.3
51. 2
52. 2
53. 3
54. 1
55. 3
56. 3

Types of Matter
Homogeneous vs. Heterogeneous
DEFINE
Homogeneous Particles are uniformly distributed
Example: sugar and water  Aqueous solution
Heterogeneous not uniformly mixed or distributed
Example: cookie dough, cement
PURE SUBSTANCES
CHEMICALLY combined
Element: CANNOT BE DECOMPOSED
Compound TWO OR MORE DIFFERENT
ELEMENTS COMBINED IN A FIX RATIO
MIXTURES
PHYSICALLY combined
Homogeneous Particles are uniformly
distributed
Heterogeneous not uniformly mixed or
distributed

DRAW ME A PICTURE AND LABEL IT (figure 1-12)
ELEMENT A
QUESTIONS
58. _____
59. _____
60. _____
61. _____
62. _____
63. _____
70.
ELEMENT B
64. _____
65. _____
66. _____
67. _____
68. _____
69. _____
MIXTURE OF A AND B COMPOUND MADE
FROM A AND B

77.
75.
76.
73.
74.
71.
72.