The Periodic Table

Mendeleev's 1869 Periodic Table

     More and more elements were being discovered, and chemists were searching for a way to organize them in predictable patterns. In 1896, the above table was presented to a select group of scientists. Russian chemist Dimitri Ivanovich Mendeleev had observed that many elements had similar properties, and that these similar properties recurred in a periodic fashion. Hence, the name 'periodic table'.

     Mendeleev's first table was based on atomic weights, rather than atomic numbers as the modern periodic table. This led to some discrepancies. For example, the mass of Tellurium was greater than Iodine by the best estimates of that time. But they didn't seem to fit the groupings he had devised. This is because although Tellurium has a greater atomic weight, it has a lower atomic number (ie, number of protons). In 1871, Mendeleev presented the new, revised periodic table as seen below.

     There were, obviously, gaps in the table. The attempt to fill in the gaps of the periods led to the discovery of many new elements. The 'natural elements', those occuring naturally in the world, fill in atomic numbers 1 (Hydrogen) through 92 (Uranium). The man-made elements, or 'trans-uranics' continue to be discovered. There are now known to be well over 110 elements, with the possibility of many more to come. The answer to the question "what makes the world" was no longer simple, and physicists began to look deeper.

Mendeleev's 1871 Periodic Table

Quarks: The Search for the Elementary Particle

The History of the Atom

The Periodic Table

The Subatomic Particles

The Quark Theory

The Future?

Links and References

<BGSOUND SRC="Mars.mid" Loop="-1"> MIDI sequence(s) from the Classical MIDI Archives - by permission (Link goes off-site)