Man's physical universe

xanabras

568 MAN IS MASTKRING HIS MATKRIAL WORLD

family. As Newlands expressed it, "the eighth element starting from

a given one is a kind of repetition of the first, like the eighth note of an

octave of music."

Independently of each other and in

ignorance of Newlands' work,

Lothar Meyer in Germany and Dmitri Ivanovitch Mendeleeff in Russia

made a thorough study of the properties of the elements and noted a

similar relationship. They proposed the law, known as the periodic

law, which states that the properties oj the elements are periodic Junctions

of their atomic weights.

Periodicity is very common in nature. The growth of trees, the

cycle of droughts, periods of large sunspots, the tides, and the full

moon all occur periodically. A flattened wheel on a railroad car produces

a periodic clatter which is a function of the distance traveled,

because every full turn of the wheel brings the flattened portion of the

wheel into contact with the track.

Mendeleeff prepared a table of the elements based upon their

periodicity in properties. He left a number of gaps in this table in

places where the progression in properties seemed to demand it,

arguing that there must be elements which had not yet been discovered.

The known character of the elements above and below these

gaps made it possible to predict the properties of the missing elements.

Mendeleeff made these predictions in 1870 for three elements, calling

them eka-boron, eka-aluminum, and eka-silicon. These elements, discovered

in 1879, 1875, and 1886, and named scandium, gallium, and

germanium, showed properties that checked remarkably closely with

those predicted by Mendeleeff. This strong support of the periodic

law was strengthened later by the discovery of all but two of the

remaining missing elements partly through the aid furnished by the

periodic table.

The periodic table is one of the most useful generalizations in chemistry,

because it is of great value in predicting the properties of elements

and in classifying chemical information.

How shall one explain this very remarkable law? One generally

expects to find a common origin or a common building material for

people, houses, or materials which are similar in properties. It is the

fact that houses are made of smaller units, such as bricks, that makes

possible such a wide variety of patterns. This complexity of structure

also makes it possible to build large or small houses of the same design,

using different numbers of bricks. If the atoms of the elements are

ultimate, no relationships should exist. The chief significance of the

periodic law is that it suggests the existence of atoms of similar, and

therefore complex, structure.

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