Edward Frankland ( )

Group 5A Elements

When the formulae of inorganic chemical compounds are considered, even a superficial observer is impressed with the general symmetry of their construction. The compounds of nitrogen, phosphorus, antimony, and arsenic, especially, exhibit the tendency of these elements to form compounds containing 3 or 5 atoms of other elements; and it is in these proportions that their affinities are best satisfied: thus in the ternal group we have: NO 3, NH 3, NI 3, NS 3, PO 3, PH 3, PCl 3, SbO 3, SbH 3, SbCl 3, AsO 3, AsH 3, AsCl 3, etc.: and in the five-atom group, NO 5, NH 4 O, NH 4 I, PO 5, PH 4 I, etc. Without offering any hypothesis regarding the cause of this symmetrical grouping of atoms, it is sufficiently evident from the examples just given, that such a tendency or law prevails, and that, no matter what the character of the uniting atoms may be, the combining power of the attracting element, if I may be allowed the term, is always satisfied by the same number of these atoms. Phil. Trans. Royal Soc. 1852

Richard Abegg ( )

Abegg’s Rule The difference between the maximum positive and negative valence of an element is frequently eight.

Nature of Light Isaac Newton ( ) Christiaan Huygens (1629 – 1695)

Properties of Waves ReflectionRefraction

Diffraction

Interference

Properties of Light Reflection Refraction

Reflection of Light CorpusclesRefraction of Light Corpuscles

Huygen Construction for Reflection Huygen Construction for Refraction Huygen’s Construction

Young’s Double Slit Experiment Thomas Young (1773 – 1829)

Laser Source for Double Slit Experiment

Interpretation of the Doubl e Slit Results

Fresnel’s Dot Augustin Jean Fresnel (1788 – 1827) Simeon Poisson (1781 – 1840)

Maxwell’s Equations James Clerk Maxwell (1831 – 1879)

Electromagnetic Radiation

Heinrich Hertz (1857 – 1894)

Light is a Wave

Blackbody Radiation

Cavities as B lackbo dies

The Ultraviolet Catastrophe Lord RayleighJames Jeans

After a few weeks of the most strenuous labor of my life, the darkness lifted and a new, unimagined prospect began to dawn. Max Planck (1858 – 1947)

Photoelectric Effect

Albert Einstein (1879 – 1955)Robert Millikan ( ) Einstein’s equation was a bold prediction, for at that time there was no evidence that Planck’s constant had any applicability outside of blackbody radiation and there were no experimental data on the [kinetic energy] as a function of frequency. Physics by Paul A. Tipler

Millikan’s Photoelectric Data

The Double Slit Experiment Revisited

Light is a Particle