1. Chapter 3
History of the Atom

2. History of Atom Part 1

3. Dalton’s Atomic Theory (1808)
All matter is made of indivisible and indestructible atoms.
All atoms of the same element are identical in their physical and chemical properties.
Atoms of different elements have different properties.
Atoms of different elements combine in simple whole-number ratios to form compounds.
Atoms cannot be subdivided, created, or destroyed when they are combined, separated, or rearranged in chemical reactions.

4. Changes to Dalton’s Theory
Are atoms actually indivisible?
Are all atoms identical?

5. The Atom
the smallest unit of an element that retains that elements properties
Made of protons, neutrons, and electrons
Can you see inside an atom?
How did they know it contains protons, neutrons and electrons?

6. Obscertainer Activity

7. History of Atom Part 2

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

9. Cathode Ray Tube
When connected to electric current the remaining the gas forms a BEAM OF LIGHT.
The beam always started at the NEGATIVE electrode and flowed to the POSITIVE electrode.
The electrode is named by what type of particle it attracts
Cathode: Negative (-)
Anode: Positive (+)

10. Cathode Ray Conclusions
1. The beam was attracted to a POSITIVE magnet.
2. The beam must be made of NEGATIVE particles.

11. JJ THOMSON DISCOVERED A NEGATIVE PARTICLE CALLED THE:
ELECTRON!

12. Plum Pudding Model

13. Plum Pudding OR Chocolate Chip Cookie

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. Types of Radiation
Radiation Type
Greek Symbol
Charge
Alpha
Beta
Gamma

16. 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

17. Rutherford’s Gold Foil Experiment

18. alpha particles shot through the gold foil
bouncing back – like hitting the target
going through – missing the target

19. 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

20. Rutherford’s Model of the Atom – + NUCLEUS EMPTY SPACE
If the atom is the size of Giants Stadium
Then the nucleus is a marble on the 50 yard line

21. History of Atom Part 3

22. **DISCOVERED THE PROTON!!
Goldstein and Wien
Used a cathode ray tube
Discovered collection of positively charged particles
**DISCOVERED THE PROTON!!

23. 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!!

24. **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!!

25. Bohr’s Model of the Atom–
ENERGY
LEVELS +
NUCLEUS

26. Bohr Models P+ no n=3 n=2 n=1 Energy Level (n) # of Electrons
Nucleus = correct number of protons & neutrons

27. How to Fill in Bohr Models

28. Element Symbols

29. Element Symbols Rule 1 First letter is capitalized
H Hydrogen C Carbon O Oxygen
Rule 2
Second letter is lower case
Cl Chlorine He Helium Ne Neon
Rule 3
Some are Latin names
Na Sodium (natrium) Fe Iron (ferrum)
Rule 4
Some elements are named for places, scientists, greek gods…
Eu Europium Am Americium

30. Hyphen Notation
The mass number is written with a hyphen after the name of the element.
Element – Mass#
Uranium – 235
Calcium – 40

31. Nuclear Symbol
The superscript indicates the mass number and the subscript indicates the atomic number. X A Z
Mass Number
Element Symbol
Atomic Number C 12 6

32. Subatomic Particles

33. Subatomic Particles PARTICLE SYMBOL CHARGE LOCATION RELATIVE MASS
PROTON
NEUTRON
ELECTRON

34. ALL ATOMS ARE ELECTRICALLY NEUTRAL
Must have same number of protons and electrons
Atomic Number: number of protons
NUMBER OF PROTONS NEVER CHANGES!
Every atom of an element has the same number of protons which makes the element unique

35. Atomic Number
Examples 3 Li
6.94
Lithium: atomic number of 3 How many protons? Hydrogen: atomic number of 1 If you add another proton, does it become positive?

36. Mass Number
Protons + Neutrons This is not the actual mass of the atom Masses on the periodic table are NOT whole numbers
Examples:
Silicon 14 protons 14 neutrons
Mass Number = ______
Fluorine 9 protons ____ neutrons
Mass number = 19

37. ELEMENT
SYMBOL
ATOMIC NUMBER
PROTONS
NEUTRONS
ELECTRONS
MASS NUMBER
Nitrogen 15 Cu 35 38 88 12 30 26

38. Isotopes and Ions

39. Isotopes
Atoms with the same number of protons and different number of neutrons

40. Hydrogen has 3 isotopes:
1 p 0 n 1 p 1 n 1 p 2 n
Hydrogen – 1
Hydrogen
Hydrogen – 2
Deuterium
Hydrogen – 3
Tritium

41. 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

42. cation – ion with a positive charge when an atom loses an electron
ION : an atom, or group of atoms, that has a net positive or negative charge.
cation – ion with a positive charge
when an atom loses an electron Na
11 protons
11 electrons
Na+
11 protons
10 electrons
anion – ion with a negative charge
when an atom gains an electron
Cl-
17 protons
18 electrons Cl
17 protons
17 electrons

43. 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

44. Summary Particle Protons Neutrons Electrons Atom Same Isotope
NEVER CHANGES!!!
Summary
Particle
Protons
Neutrons
Electrons
Atom
Same
Isotope
DIFFERENT
Ion

45. Average Atomic Mass

46. Relative Atomic Mass Atomic Mass Unit
Carbon is the standard for all masses on the periodic table.
Carbon: 6 p and 6 n = 12 amu
Atomic Mass Unit
Periodic table lists weighted average atomic masses of elements (like a GPA calculation)

47. Final Grade Calculation

48. Calculation AVERAGE Atomic Mass
Steps: 1. Percent to a decimal 2. Multiply by mass 3. ADD IT UP!
75% 133Cs
20% 132Cs
5 % 134Cs