1. Atoms, Molecules and Ions
Chapter 2

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.
HgO  Hg + O
433.2 g g g

3. 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.
Compounds are composed of atoms of more than one element. The relative number of atoms of each element in a given compound is always the same.
Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions.

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

5. Cathode Ray Tube
Scientists studied the flow of electric current in a glass vacuum tube with electrodes at each end.
The electrode is named by what type of particle it attracts
Cathode: Negative (-)
Anode: Positive (+)
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.

6. JJ THOMSON DISCOVERED A NEGATIVE PARTICLE CALLED THE ELECTRON!
1897 JJ Thomson used magnets to deflect the beam proving that particles had a NEGATIVE CHARGE.
JJ THOMSON DISCOVERED A NEGATIVE PARTICLE CALLED THE ELECTRON!

7. Now with the knowledge of electrons, and knowing the atom is neutral, there must be a particle that is positive to balance the negative charge.
A small paddle wheel was placed inside and it rolled toward the anode, providing evidence that some PARTICLE MUST BE STRIKING THE WHEEL to make it move.

8. CRT Video

9. Plum Pudding Model

10. Plum Pudding OR Chocolate Chip Cookie

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

12. 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

13. Oil Drop Experiment Video

14. Radioactivity Becquerel Curie
discovered RADIATION
uranium would expose photographic plates in the dark
The properties of an element changed as it gave off radiation
Curie
Discovered radium and polonium
The radioactive emissions of alpha, beta and gamma rays were identified.

15. (Uranium compound)

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.

18. Rutherford’s Gold Foil Experiment

19. MOST particles went through the gold foil
Rutherford: It’s like shooting a cannon at a piece of tissue paper and having it bounce back at you!
MOST particles went through the gold foil
SOME particles BOUNCED back

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
If the atom is the size of Giants Stadium
Then the nucleus is a marble on the 50 yard line

23. **DISCOVERED THE PROTON!!
Goldstein and Wien
Cathode Ray Tube with perforated cathode
Discovered collection of positively charged particles
**DISCOVERED THE PROTON!!

24. Chadwick’s Experiment - 1932
Found that alpha particles shot at beryllium made a beam form
The beam had the same mass of a proton but was electrically neutral
**DISCOVERED THE NEUTRON!!

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

28. Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons X A Z
Mass Number
Element Symbol
Atomic Number
Isotopes: atoms of the same element (X) with different numbers of neutrons in their nuclei 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. diatomic molecule: contains only two atoms
Molecule: an aggregate of two or more atoms in a definite arrangement held together by chemical bonds H2
H2O
NH3
CH4
diatomic molecule: contains only two atoms
H2, N2, O2, Br2, HCl, CO
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. monatomic ion: contains only one atom
Na+, Cl-, Ca2+, O2-, Al3+, N3-
polyatomic ion: contains more than one atom
OH-, CN-, NH4+, NO3-

35. Do You Understand Ions? Al How many protons and electrons are in ?27 13 ? 3+
13 protons, 14 neutrons, 10 (13 – 3) electrons
How many protons and electrons are in Se 78 34 2- ?
34 protons, 44 neutrons, 36 (34 + 2) electrons

36. 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)

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