Lecture, Wednesday, August 28, 2002

Today we started Chapter 2 by taking a tour of several of the early experiments that resulted in the characterization of the electron (cathode ray tube experiment by Thompson), the charge on an electron (Millikan), the current view of atom (Rutherford).

While you are not expected to know the details of the experiments I do want you to know the names of the three subatomic particles: electrons, protons and neutrons; their charge (-, + and 0 respectively), their location in an atom, their approximate size, and their masses in atomic mass units (very small, ~1 u, ~1 u).

I introduced the term atomic number (the number of protons in an element), mass number (the number of protons and neutrons) and isotope (an atom of an element with the same number of protons but a different number of neutrons).

I introduced the concept of relative atomic weights, the number below the element's symbol in the periodic table. I defined the relative atomic mass (u) in terms of grams;

1 u = 1.66 x 10 -24 g

We looked at the notation for isotopes.