Knowledge of the chemical elements - as opposed to the metaphysical elements of ancient Greece, India, and China, dates back only a few centuries. In the 18th century the French chemist Antoine Lavoisier revived Robert Boyle's use of the word "element" for substances that could not be broken down into simpler substances. Over the next 75 years many new elements were discovered, and some substances previously thought to have been elements were actually shown to be chemical compounds.
It was also discovered some elements are similar to others. Sodium and Potassium, isolated in the early 1800's by Humphrey Davy, are both soft metals that react violently to water to produce alkaline solutions.
One quality being catalogued at that time was atomic weight. Using various analytical skills, nineteenth century chemists gradually catalogued the atomic weights of various elements with more accuracy. the weight of hydrogen was taken as 1, with other elements related to it.
The Russian chemist Dmitry Mendeleyev first proposed the modern periodic table of elements in 1869. He arranged the elements in tabular form in order of increasing weight. Where there were large gaps between two elements he assumed a new undiscovered one. As the elements were also arranged in families (columns) this enabled him to predict the properties of the undiscovered elements with great accuracy (like Sodium and Potassium referred to earlier) This major theoretical breakthrough provided the necessary classification system by which the properties of all the atomic elements could be mapped out.
Element, chemical - excellent basic introduction at Science Clarified to the chemical elements; includes an explanation of the periodic table
Periodic table - on wikipedia. Includes links to each element
The Periodic Table of Chemical Elements - a basic html table - lists all the elements
The nuclei of hydrogen and most helium atoms were formed about one microsecond and three minutes respectively after the original Big Bang. Heavier elements were made later, by nuclear reactions in the core of stars - the heaviest reactions being formed inside exploding stars.
It is estimated that the rate of element formation peaked sharply at around 11,000 million years ago. Galaxies around 6000 million light years distant (redshift z=0.5) show more blue, element making stars than nearer (closer to us in time) galaxies do.
The average age of those elements heavier than hydrogen, found in meteorites and on earth, is, according to radiometric dating, around 10,000 million years, although there were significant late injections from other exploding supernovae at 4650 ago and 4,550 million years ago, shortly before the formation of the Solar System.
The average age of elements in the spiral arms of the galaxy, where element making has continued during the past 4,550 million years, is around 9,000 million years. In globular clusters and in the center of the galaxy, elements may be somewhat older.
Nigel Calder, Timescale - an Atlas of the Fourth Dimension , pp.226-7 (Hogarth Press, London)
Heavy Element Fusion
the mandala of the elements
from Edward Haskel, ed. Unified Science
CHAPTER 7: ENERGY- Chemistry, Crises and the Chakras- by Arnold Keyserling and R.C.L. - gives a metaphysical approach to the elements and periodic table