1. Chapter 4: The Structure of the Atom 4.1 The Structure of the Atom
Democritus ( B.C.) was the first to use the term atom. He, and the atomists, described atoms as the indivisible particle.
Aristotle ( B.C.) critisized Democritus by asking what held atoms together, developed the idea of earth, fire, water and wind as the 4 elements of all natural substances.

2. 4.1 Continued
John Dalton, ( ) proposed, in 1803, the atomic theory.
1-Matter is composed of small particles called atoms.
2-Atoms are indivisible and indestructable.
3-Atoms of given elements are identical.
4-Atoms of a specific element are different from atoms of other elements.
5-Different atoms combine in simple whole number ratios to form compounds.
6-In chemical reactions, atoms are separated, rearranged or combined.
The red texted items were mistakes.

3. Conservation of Mass
Mass is not created nor is it destroyed, it is only conserved.

4. 4.2 Defining the Atom
The scanning tunneling microscope can actually image individual atoms.
Sir William Crookes and JJ Thomson discovered the electron...this exposed the flaw of the 'indivisible atom' of Dalton.
The cathode ray tube was used to study the electron.
JJ Thomson discovered the charge-to-mass ratio and Robert Millikan discovered the charge of the electron, with the oil-drop experiment.
Using the charge and charge to mass ratio, Millikan estimated the electon mass as 9.1 x grams.

6. 4.2 Models of the Atom
JJ Thomson developed the plum-pudding model of the atom.
Rutherford developed his concept of the nucleus with the gold foil experiment.(txt p 112)
Sir James Chadwick discovered the neutron in 1932.

7. Rutherford's Experiment

8. Properties of Subatomic Particles
Particle Relative Charge Relative Mass
Electron − /1840
Proton
Neutron

9. 4.3 How Atoms Differ
Atomic Number is the number of protons in an atom....since atoms are neutral, it is also the number of electrons.
Mass Number is the number of protons and neutrons added together.
Isotopes are the different forms of the same atom, with different numbers of neutrons and different masses...the same atoms always have the same atomic number.

10. Mass of Atoms
The Atomic mass unit is used to provide a relative mesure of mass of atoms and subatomic particles.
Atomic mass is the weighted average of all isotopes of an atom.
1. Multiply the mass of an isotope times the decimal form of its abudance.
2. Repeat for each isotope.
3. Add the totals of each isotope to get the atomic mass.