Page 101 - Bruno Linder Elementary Physical Chemistry

August 18, 2010 11:36 9in x 6in b985-ch08 Elementary Physical Chemistry

86 Elementary Physical Chemistry

Plot of variation of C V with T.
Fig. 8.1

8.2.4. Wave or Particle?
So what is light? The photo-electric effect clearly established light to be
particle-like. Young’s experiment on interference diffraction and Maxwell’s
theory of electromagnetic radiation clearly established light to be wave-like.
How could the same entity, light, be such a contradictory thing?

8.3. The Rutherford Atom
The Rutherford experiment (∼1911) is one of the most important experi-
ments ever performed, for it established unequivocally the structure of the
atom (Fig. 8.2).

(1) The experimental set-up. In this experiment, a narrow beam of α rays
from a radioactive source (radium) was aimed at a very thin gold foil.
Behind the gold foil was a screen coated with a chemical (zinc sulfide),
which has the following property: it flashes when hit by an α-particle.

Note: Some naturally occurring heavy atoms (e.g. uranium, radium,
polonium, etc.) have the ability to emit rays. The rays are of three
types: α-rays, β-rays and γ-rays. The α-rays are bare positively
charged helium nuclei (helium atoms stripped of the electrons);
β-rays are electrons; γ-rays are the most energetic forms of electro-
magnetic radiation.