1. Quiz: October 19, 2004
How many significant figures are in the number ?
What is the density of an object with a mass of 1.0g and a volume of 2.00 ml?
In the experiment: What is the effect of caffeine on the pulse of people 20 and older? Identify the independent and dependent variables.
What question are you asking for your science fair project. Underline the independent variable, circle the dependent variable.
Who is responsible for the development of the “modern” atomic theory.
5 sig. digs.
1.0g/2.0 ml = 0.50 g/mL
Amount of caffeine = independent variable;
pulse rate = dependent variable
What is the effect of ___ on O?
Charles Dalton

2. Chapter 4 Atomic Structure www.ec.njit.edu.atoms.files pictures.
Democritus
Dalton
Thomson
Rutherford
Bohr
Modern / Wave Atomic Theory

3. Dalton’s Atomic Theory
Elements are made of tiny particles called atoms.
All atoms of a given element are identical.
All atoms of a given element are different from the atoms of other elements.
Atoms can combine with each (in small whole number ratios) other to form different compounds. (ex: NO, NO2, N2O)
Atoms are indivisible.
Atoms can be divided. Electrons are
transferred during chemical reactions,
and nuclear reactions are possible, though rare.
Atom = indivisible sphere

4. James Chadwick and Walter Bothe both discovered the proton.
In 1932 Chadwick observed that beryllium, Be, when hit with alpha particles, released an unknown radiation that in turn ejected protons from the nuclei of various substances. Chadwick interpreted this radiation as being composed of particles of mass approximately equal to that of the proton, but without electrical charge--neutrons.
Atom = sphere containing positive,
negative, and neutral charges + + + X Be - Li
X-1

5. Summary Democritus: Atom Aristotle: Continuous Matter
Proust: the Law of Definite Composition
Lavosier: the Law of Conservation of Matter
Dalton: “Modern” Atomic Theory
JJ Thompson: Discovery of Electrons
Millikin: Charge/Mass ratio of electrons
Moseley: Discovery of Protons/Atomic Number
Chadwick and Bothe: Discovery of Neutrons

6. Rutherford’s Team: Neils Bohr, Hans Geiger, Ernest Marsden.
Gold Foil Experiment.
most of the alpha
particles went straight
through, some were
deflected by a “large” mass.
The PROTON was discovered. +
Atom =
sphere containing positive,
negative charges, and some number
of neutral particles, depending upon
the isotope. The positive charges were
located in the nucleus.

7. The Nuclear Atom Gold Foil Experiment. + most particles
go straight through.

8. The Nuclear Atom Gold Foil Experiment. + most particles
go straight through.
Some are deflected
by the nucleus

9. Summary Democritus: Atom Aristotle: Continuous Matter
Proust: the Law of Definite Composition
Lavosier: the Law of Conservation of Matter
Dalton: “Modern” Atomic Theory
JJ Thompson: Discovery of Electrons
Millikin: Charge/Mass ratio of electrons
Moseley: Discovery of Protons/Atomic Number
Chadwick and Bothe: Discovery of Neutrons
Rutherford: The Nuclear Atom

10. Henri Becquerel
Found that matter containing uranium exposed sealed photographic film. +

11. Isotopes:
J.J. Thomson observed two kinds of neon atoms. neon-20 and neon-21
Both neons are chemically identical, but their masses differ.
Atom =
sphere containing positive,
negative charges, and neutral particles.

12. Isotopes neutrons! What causes the extra mass? Isotope Atomic number
Number of protons
Number of electrons
Mass number
H-1 1
H-2 2
H-3 3
P-31 15 31
+ 0 = 1
+ 1 = 2
+ 2 = 3
+ 16 = 31

13. Time-Line of Discovery
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