1. Atoms, Molecules and Ions
Chapter 3

2. Foundations of Atomic Theory
Law of conservation of mass: Antoine Lavoisier
Mass is neither created nor destroyed. The total mass of a compound must be the same as the total mass of individual elements.
Law of definite composition: Joseph Proust
a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound
HgO  Hg + O
433.2 g g g
Sugar: 42.1 % Carbon
51.4 % Oxygen
6.5 % Hydrogen
Whether you have a teaspoon or a truckload!

3. Law of Conservation of Mass
16 X
8 Y +
8 X2Y
Law of Conservation of Mass

4. Law of multiple proportions: John Dalton
Applies to different compounds made from the same elements
The mass ratio for one of the elements that combines with a fixed mass of the other element can be expressed as a whole number ratio.
H2O H2O2
Water Peroxide
2g H g H
16g O :2 Ratio g O

5. Law of Multiple Proportions2
Law of Multiple Proportions

6. Dalton’s Atomic Theory (1808)
Elements are composed of extremely small particles called atoms.
All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements
Atoms cannot be subdivided, created or destroyed

7. Dalton’s Atomic Theory (1808) cont’d
Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
5. Chemical reactions only involve the rearrangement of atoms.

8. JJ Thomson’s Cathode Ray Tube
Negatively Charged
Electrode
Positively Charged
Electrode

9. Cathode Ray Tube
Scientists studied the flow of electric current in a glass vacuum tube with electrodes at each end.
When connected to electric current the remaining gas glowed forming a BEAM OF LIGHT.
The beam always originated at the NEGATIVE electrode and toward the POSITIVE electrode.
1897 JJ Thomson used magnets to deflect the beam proving that particles had a NEGATIVE CHARGE.

10. JJ THOMSON DISCOVERED A NEGATIVE PARTICLE CALLED THE ELECTRON!

11. CRT Video

12. Plum Pudding Model

13. Plum Pudding OR Chocolate Chip Cookie

14. Robert A. Millikan Performed the Oil Drop Experiment
Determined the exact charge of an electron

15. Thomson’s charge/mass of e- = -1.76 x 108 C/g
Measured Charge of e-
(1923 Nobel Prize in Physics)
e- charge = x C
Thomson’s charge/mass of e- = x 108 C/g
e- mass = 9.10 x g

16. Oil Drop Experiment Video

17. Ernest Rutherford’s Gold Foil Experiment
Set up Gold Foil with a detection sheet around it.
Set up radioactive source emitting alpha particles.
ALPHA PARTICLES shot at gold foil.
MOST particles went through the gold foil
SOME particles BOUNCED back

18. Rutherford’s Gold Foil Experiment

20. Gold Foil Conclusions The atom is made up of mostly EMPTY SPACE
The center of the atom contains a POSITIVE CHARGE
Rutherford called this positive bundle of matter the NUCLEUS

21. Gold Foil Experiment Video

22. Rutherford’s Model of the Atom
atomic radius ~ 100 pm = 1 x m
nuclear radius ~ 5 x 10-3 pm = 5 x m
If the atom is the size of Giants Stadium
Then the nucleus is a marble on the 50 yard line

23. Ob-scertainer
You can’t see something, but you know it’s there… you feel it moving… How is it moving?
Do your best to determine the movement of the “particle” in your containers

24. Ob-scertainer Solutions#1 #2 #3 #4 #5 #6 #7 #8 #9
#10
#11
#12

25. **DISCOVERED ENERGY LEVELS!!
Niels Bohr – 1913
Developed a new diagram of the atom
Electrons can only be at certain energies
Electrons must gain a specific amount of energy to move to a higher level, called a quantum
**DISCOVERED ENERGY LEVELS!!

26. Bohr’s Model of the Atom

27. Subatomic Particles (Table 2.1)
mass p = mass n = 1840 x mass e-

28. X H H (D) H (T) U Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei
Mass Number X A Z
Element Symbol
Atomic Number H 1
H (D) 2
H (T) 3 U
235 92
238

30. Do You Understand Isotopes?
How many protons, neutrons, and electrons are in C 14 6 ?
6 protons, 8 (14 - 6) neutrons, 6 electrons
How many protons, neutrons, and electrons are in C 11 6 ?
6 protons, 5 (11 - 6) neutrons, 6 electrons

31. Period
Group

32. A diatomic molecule contains only two atoms
A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds H2
H2O
NH3
CH4
A diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
A polyatomic molecule contains more than two atoms
O3, H2O, NH3, CH4

33. cation – ion with a positive charge
An ion is an atom, or group of atoms, that has a net positive or negative charge.
cation – ion with a positive charge
If a neutral atom loses one or more electrons
it becomes a cation. Na
11 protons
11 electrons
Na+
11 protons
10 electrons
anion – ion with a negative charge
If a neutral atom gains one or more electrons
it becomes an anion.
Cl-
17 protons
18 electrons Cl
17 protons
17 electrons

34. A monatomic ion contains only one atom
Na+, Cl-, Ca2+, O2-, Al3+, N3-
A polyatomic ion contains more than one atom
OH-, CN-, NH4+, NO3-

35. How many protons and electrons are in
Do You Understand Ions?
How many protons and electrons are in Al 27 13 ? 3+
13 protons, 10 (13 – 3) electrons
How many protons and electrons are in Se 78 34 2- ?
34 protons, 36 (34 + 2) electrons

38. Relative Atomic Mass Atomic Mass Unit
One atom is the standard – Carbon
Mass of other elements are based off of the standard
Carbon: 6 p and 6 n = 12 amu
Atomic Mass Unit
1/12 mass of Carbon atom
Periodic table lists weighted average atomic masses of elements (like a GPA calculation)

39. Calculation AVERAGE Atomic Mass
75% 133Cs
20% 132Cs
5 % 134Cs
Steps: 1. Percent to decimal 2. Multiply by mass 3. Add it up!