1. Atomic Theory Chapters 3, 11 & 12 KEY VOCABULARY: Atom Alpha Radiation
Ion Beta Radioactivity
Isotope Gamma Half-Life
Proton Wavelength Quark
Neutron Frequency Lepton
Electron Energy Fundamental Particle

2. Atomic Theory Chapters 3, 11 & 12 Unit Objectives:
Explore the discovery and characteristics of subatomic particles:
electrons,
protons,
neutrons, and
fundamental particles (quarks, leptons & gluons).
Understand the structure of the atom and its relationship to radiation.

3. Ancient Philosophies (Earliest Records)
c. 400 B.C. - Ancient Greek Philosophers
Aristotle
matter is continuous (or infinitely divisible)
all matter is made of “hyle”
different types of matter are the result of varying levels of moisture, dryness, heat and cold on hyle
Democritus
matter is made of tiny particles & empty space
“atomos” (gr. - “indivisible”)
different types of matter are composed of different kinds of atoms

4. Ancient Philosophies (Ancient Greece)
Ancient Greece – NO EXPERIMENTS (two-class system)
The upper class felt it beneath them to perform manual labor.
The lower class (plebeians) were not allowed to think or express rational thought
Experiments require work with both the hands and the mind

5. Common Perception (400 B.C. - 1000 A.D.)
The general public blindly accepts Aristotle’s philosophy of matter.
Granted, most people living in these centuries were too concerned with feeding themselves and protecting themselves from wild animals and barbarians to care about the structure of matter...

6. Common Perception (1000 A.D. - 1700’s)
People still largely believe in Aristotle’s “pile of hyle”.

7. Science is "Born" (17th Century) The Alchemists
Tried to turn ordinary materials into gold.
Failed to make gold, BUT…
Succeeded in establishing many experimental techniques and systems of notation & symbols.

8. Science is "Born" (18th & 19th Centuries) Foundational Ideas
Sir Isaac Newton & Robert Boyle
(questioned Aristotle)
Antoine LaVoisier
- Law of Conservation of Matter
Joseph Proust
- Law of Definite Proportions
John Dalton
- Law of Multiple Proportions

9. Modern Atomic Theory 19th Century (That’s the 1800’s)
Modern Atomic Theory - John Dalton
1. All matter is composed of atoms.
2. Atoms of the same element are identical.
3. Atoms of the different elements are not alike.
4. Atoms unite in simple ratios to form compounds.

10. While Dalton’s four point theory was a
Dalton's Flaws
Revealed near the turn of the 20th century
While Dalton’s four point theory was a
vast improvement and forms the basis
for much of our current understanding of
matter, it did contain two definite flaws…

11. Dalton's Flaws Revealed near the turn of the 20th century
FLAW #1 – Dalton’s chose the word “atom” and meant it literally. (In Greek the word atomos means indivisible.) It was intended to express the belief that these smallest pieces of each element could not be broken down into anything smaller.
Of course, we now know that “atoms” are NOT indivisible, and can be broken down into protons, neutrons, electrons, and even smaller particles such as quarks.

12. Dalton's Flaws Revealed near the turn of the 20th century
FLAW #2 – Dalton stated that atoms of the same element are identical.
We now know that within an element, several different isotopes may exist. An element’s identity is established by its number of protons, but the number of neutrons, and in turn, the mass of atoms of the same element may differ.

13. MODERN MATTER(S)… Our Adventure Begins... 1800 – 2007…and beyond!
Since Dalton published his theory, our understanding of matter has developed at an ever-accelerating pace. Rudimentary laws of chemistry have been developed. The structure of atoms has been explained. The impact of how electrons affect chemical change is largely understood. Yet, while scientists have discovered a great deal about the particles which make up the atom, the structure and interactions between these “fundamental particles” is the subject of much ongoing research….

14. Early Atomic Experiments
Turn of the 20th Century
J.J. Thomson – Cathode Rays and Magnetic Fields
Robert Millikan’s Oil Drop Experiment
Rutherford’s Gold Foil Experiment
Henry Moseley – x-rays and Atomic Number
Walther Bothe & James Chadwick – NEUTRONS!

15. J.J. Thomson
1897
cathode rays & - +
magnetic fields

16. J.J. Thomson – what he did & what he saw
Exposed cathode rays to magnetic fields
Hoped to separate charges from rays
Rays were deflected WITH the charges

17. J.J. Thomson – what he concluded
Rays were composed of negatively charged particles
He called these particles “corpuscles”
These particles came to be known as “electrons”
(Note: Thomson was awarded a Nobel Prize in 1906)

18. Robert Millikan
1909

19. Robert Millikan – what he did & saw
Adjusted the charge on the plates until gravity and charge balanced and oil droplets hovered
Calculated the charge on each droplet

20. Robert Millikan – what he concluded
Observed that charges were different, but had a common denominator
Determined the charge on an electron
(1.6 x Coulombs)
(Note: Millikan was awarded a Nobel Prize in 1923)

21. Ernest Rutherford
1911

22. Ernest Rutherford – what he did & saw
(Experiment conceived by Rutherford but conducted by grad students Hans Geiger and Ernest Marsden)
Fired alpha particles at gold foil
Saw that most particles passed straight through the foil, but some were deflected sharply

23. Ernest Rutherford – what he concluded
The atom has a very small mass center
This tiny mass center is surrounded by lots of empty space

24. Henry Moseley
1914

25. Henry Moseley – what he did & saw
Experimented with x-ray tubes by changing the metal used for the anode
Measured the wavelengths of the resulting x-rays

26. Henry Moseley – what he concluded
Each different metal is made of its own unique kind of atoms
Each element’s atoms have a characteristic number of protons in their nuclei (atomic number)

27. Walther Bothe & James Chadwick a a a a
Beryllium-9
Parrafin Wax - - + +

28. Walther Bothe & James Chadwick – what they did & saw
Bombarded beryllium-9 with alpha particles.
This gave off high energy rays which were unaffected by a magnetic field.
These rays, when directed at parrifin wax, displaced high energy protons

29. Walther Bothe & James Chadwick – what they concluded
Bothe didn’t know what conclusion to draw, but set the stage for Chadwick two years later
Chadwick repeated Bothe’s experiment and concluded that this particle with similar mass as a proton, but with no charge, must be the third subatomic particle which had been proposed for over 10 years by others, but was previously unproven.

30. Inside the Atom Atomic Number Mass Number Atomic Mass
number of protons in the nucleus of an atom. (defines an element)
number of protons plus neutrons in the nucleus of A SPECIFIC ISOTOPE!
weighted average of the masses of all isotopes of an element

31. Inside the Atom So, how do we know…
…the number of protons?
…the number of neutrons?
…the charge?
= the atomic number (Z)
p+ + n = Mass # (A)
Charge = p+ - e-

32. Inside the Atom So, how do we know…
…the average atomic mass? (Simple vs. Weighted average: What is the average age of people in this room?)
Chemistry: A Modern Course – p. 137, #8 & 9

33. Inside the Atom So, how do we know…
…the relative abundance (percentage) of each isotope?
MASS SPECTROMETRY

34. ATOMIC THEORY Radiation vs. Radioactivity
Radioactivity – the spontaneous decay of an unstable nucleus. (Why does this happen? Why DOESN’T it happen sometimes?????) Radiation – energy carried by streams of particles and/or vibrations though a medium (waves). All radioactivity produces radiation, but NOT all radiation comes from radioactivity! (Radiation produced by radioactive processes is called nuclear radiation.) MAKE SURE YOU HAVE NOTES ON PROPERTIES OF IONIZING RADIATION

35. ATOMIC THEORY Radiation and Identifying Elements
Spectroscopy – the “fingerprints” of the elements. Explanation (0:49-4:48) Because each element has a unique arrangement of electrons, each element gives off a unique light pattern when its atoms are excited. These light patterns may be difficult to distinguish with the naked eye, but with the help of a spectroscope we can identify a specific element by its SPECTRUM.

36. ATOMIC THEORY Properties of Radiation
Wavelength – distance from the peak of one wave to the peak of the next wave. (May also be measured from one trough to the next trough.)
Frequency – number of waves passing a point each second
Photon – a “particle” of light
c =ln
E=hn