Development of Periodic Table
Law of Triads
Law of Octaves
Elements could be classified into groups of three, or triads.
Trends in physical properties such as density, melting point,
and atomic mass were observed.
Arranged the 62 known elements into groups of seven
according to increasing atomic mass. 
He proposed that an eighth element would then repeat the
properties of the first element in the previous group.
J.W. Döbereiner (1829)
J.A.R. Newlands (1864)
Lothar Meyer (1830 – 1895)
Invented periodic table independently of Mendeleev
his work was not published until 1870 - one year after Mendeleev's
The Periodic Table
     “As new elements were discovered, their atomic masses were determined, and the way each reacted with other substances was studied.  Chemists began to notice families of elements that showed similar behavior.  As early as 1829 Johan Döbereiner (1780-1849) had introduced the idea of triads of elements (groups of three):  thus lithium, sodium, and potassium, all similar metals, formed one group, and they tended to behave in the same way.  The Russian chemist Dmitri Mendeleyev (1834-1907) observed that elements listed in order of atomic mass showed regularly (or periodically) repeating properties.  He announced his Periodic Law in 1869 and published a list of known elements in a tabular form.  He had the courage to leave gaps where the Periodic Law did not seen to fit, predicting that new elements would be discovered to fill them.”

The modern periodic table has evolved through a long history of attempts by chemists to arrange the elements according to their properties as an aid in predicting chemical behavior.

Johannes Döbereiner in circa 1800 noticed that many of the known elements could be grouped in triads, sets of three elements that have similar properties.
In the early 1800's Dobereiner noted that similar elements often had relative atomic masses, and DeChancourtois made a cylindrical table of elements to display the periodic reoccurrence of properties.
By the mid-nineteenth century, John Newlands hypothesized that the chemistry of the elements might be related to their masses and arranged the known elements in order of increasing atomic mass and found  that every seventh element had similar properties.  Newlands suggested that the elements could be classified into octaves, corresponding to the horizontal rows in the main group elements, but this did not seem to work for elements heavier than calcium.

Cannizaro determined atomic weights for the 60 or so elements known in the 1860s, then a table was arranged by Newlands, with the elements given a number in series in order of their atomic weights, beginning with Hydrogen.

This made evident that "the eighth element, starting from a given one, is a kind of repetition of the first", which Newlands called the Law of Octaves.

Both Meyer and Mendeleyev constructed periodic tables independently that are credited as being the basis of the modern table. Meyer was more impressed by the periodicity of physical properties, while Mendeleyev was more interested in the chemical properties.
“No one foresaw the discovery of an entirely new group of elements in the 1890’s.  They were added as a separate column.  The periodic table did not immediately have an impact on chemical theory until the discovery of missing elements.”

The periodic table achieved its modern form through the work of Julius Meyer and Dimitri Mendeleev, who focused on the relationships between atomic mass and various chemical properties.

Mendeleyev published his periodic table & law in 1869 and forecast the properties of missing elements, and chemists began to appreciate it when the discovery of elements predicted by the table took place. Periodic tables have always been related to the way scientists thought about the shape and structure of the atom, and has changed accordingly.
Dimitri Mendeleyev
     "...if all the elements be arranged in order of their atomic weights a periodic repetition of properties is obtained." - Mendeleyev

Mendeleev had gained considerable notoriety by boldly predicting chemical properties of certain undiscovered elements.

In 1869, they independently proposed essentially identical arrangements of the elements.  The periodic law appears to have been discovered by at least six people independently within the one decade - Mendeleyev, Lothar Meyer, Hinrichs, Odling, Newlands, and De Chancourtois.

Meyer aligned the elements according to periodic variations in simple atomic properties such as atomic volume, which he obtained by dividing the atomic mass (molar mass) in grams per mole by the density of the element in grams per cubic centimeter:

            molar mass (g/mol)
                  density (g/cm3)                  =       molar volume (cm3/mol)

The `modern' periodic table is very much like a later table by Meyer, arranged, as was Mendeleyev's, according to the size of the atomic weight, but with Group 0 added by Ramsay. Later, the table was reordered by Mosely according to atomic numbers (nuclear charge) rather than by weight.

-Eyewitness Science “Chemistry” , Dr. Ann Newmark, DK Publishing, Inc., 1993, pg 23

Newlands (English chemist) idea was rejected by the scientific community for ~20 years.  In 1887, Newlands accepted the Davy Medal from the Royal Society of Great Britain.

1800      Only 30 elements had been isolated and identified.
1870      60 known elements

Lothar Meyer (German chemist)