1. Chapter Four The Structure of the Atom (p. 87-97)
Section 4.1 “Early Theories of Matter”
Section 4.2 “Subatomic Particles and the Nuclear Atom”

2. Section 4. 1 “Early Theories of Matter” Section 4
Section 4.1 “Early Theories of Matter” Section 4.2 “Subatomic Particles…”
Democritus (p. 88)
John Dalton (p. 89)
William Crookes (p. 92)
J. J. Thomson (p. 92)
Robert Millikan (p. 94)
Ernest Rutherford (p. 94)
James Chadwick (p. 96)
Niels Bohr (p. 127)

3. The Greeks Democritus and Leucippus
Pupil and Teacher
Earliest notions of atomic theory
Based in philosophy, not scientific research
Most of their writings are lost; we look to the writing of others such as Lucretius (who lived over 300 years later) - "De Rerum Natura" (On the Nature of Things)

4. Democritus’s Ideas
Matter is composed of empty space through which atoms move.
Atoms are solid, homogeneous, indestructible, and indivisible. (“atomos” = can’t be cut)
Different kinds of atoms have different sizes and shapes.
The differing properties of matter are due to the size, shape, and movement of atoms.
Apparent changes in matter result from changes in the groupings of atoms and not from changes in the atoms themselves.

5. Aristotle (384-322 B. C.) One of the most influential philosophers.
Wrote extensively on many subjects, including politics, ethics, nature, physics, and astronomy.
Most of his writings have been lost through the ages.
Aristotle was influential in the rejection of the concept of the atom.

6. Democritus & Aristotle http://dbhs. wvusd. k12. ca

7. Aristotle
Rediscovery of Aristotle’s writings around 1200 a.d. led to the Catholic church equating atomism with Godlessness and heresy
The atomic theory was brushed aside due to conflicts with the church establishment (and Aristotle’s philosophical legacy).

8. John Dalton ( )
research focused on gases (vapor pressure, solubility, and properties of gas mixtures)
“father of atomic theory”
combined his own research with that of many others to propose his theory of the atom in 1803 to answer the law of conservation of mass and the law of definite proportions.
most were not new ideas, but overall it was by far the most clear, comprehensive explanation of the nature of atoms to date

9. Dalton’s Atomic Theory http://dbhs. wvusd. k12. ca
All matter is composed of extremely small particles called atoms.
All atoms of a given element are identical, having the same size, mass and chemical properties. Atoms of a specific element are different from those of any other element.
Atoms cannot be created, divided into smaller particles, or destroyed.
Different atoms combine in simple whole-number ratios to form compounds.
In a chemical reaction, atoms are separated, combined, or rearranged.

10. Cathode Ray Tube (CRT)
A tube used by researchers to study the relationship between mass and charge.
Figure 4-7 (p. 92)
Cathode—
Anode—
William Crookes noticed a flash of light in the CRT
Multiple experiments helped determine the properties of the cathode rays. (figure 4-8, p. 93)

11. Cathode Ray Tube (CRT)

12. Cathode Ray Tube (CRT)

13. Cathode Ray Tube (CRT)
Cathode rays were actually a stream of charged particles
The particles carried a negative charge
The following were properties of the cathode ray that researches wanted to know:
The value of the negative charge
The mass of a single CRT particle

14. Cathode Ray Tube (CRT)

15. Cathode Ray Tube (CRT)

16. Cathode Ray Tube (CRT)

17. J. J. Thomson CRT experiments
Determined the charge to mass ratio of the cathode ray particle
Concluded that the mass of the particle was 1/2000 the mass of a hydrogen atom, the smallest atom
Identified the first subatomic particle,
the electron.
Figure 4-10, p. 94
“Plum Pudding Model of the Atom”

18. Robert Millikan http://dbhs. wvusd. k12. ca

19. Robert Millikan http://dbhs. wvusd. k12. ca

20. Robert Millikan & J. J. Thompson
The value of the negative charge (electron)
   elementary charge = 1.6× coulombs
The mass of a single CRT particle (electron)
me = 9.1 x kg or 9.1 x g

21. Thompson’s Model – “Plum-Pudding” Model

22. Rutherford’s Gold Foil Experiment http://wisp11. physics. wisc

23. Rutherford’s Gold Foil Experiment

24. Ernest Rutherford http://dbhs. wvusd. k12. ca
Gold foil experiment
Figure 4-11, p. 95
Concluded that an atom is mostly empty space through which the e- move.
Concluded that all the mass and positive charge of the atom is in a very tiny, dense region called the nucleus
Figure 4-12, p. 95
“The Nuclear Model of the Atom”

25. Nucleons http://www.encyclopedia.com/html/C/ChadwickJ1.asp
Protons
E. Rutherford determined that the nucleus contained positively charged particles called …
A subatomic particle that carries a charge equal to but opposite that of an electron…+1
Neutrons
Discovered by James Chadwick
A subatomic particle that carries no charge
Subatomic particles in the nucleus are ____.

26. Neutron = Proton + Electron Helps to hold the atom together

27. Bohr Model of the Atom http://www. colorado

28. Bohr Model of the Atom http://csep10. phys. utk

29. Atomic Model of Nitrogen

30. Atoms
The smallest particle of an element that retains the properties of the element is an atom.
Figure Atoms consist of a “cloud” of fast moving, negatively charged electrons surrounding a tiny, extremely dense nucleus containing positively charged protons and neutrally charged neutrons. The nucleus contains virtually all of the atoms’s mass, but occupies only an extremely small part of the volume of the atom.

31. Table 4-1 Properties of Subatomic Particles (p. 97)
Symbol
Location
Relative
Electrical
Charge
Relative mass
(amu)
Actual mass
(g)
Electron e-
outside the nucleus 1-
9.11x10-28
Proton p+
in the nucleus 1+ 1
1.673x10-24
Neutron no
In the nucleus
1.675x10-24

32. Atom Models

33. Atom Models

35. Quarks?