1.1 What is Chemistry?

6.1. History of the Periodic Table http://www.ck12.org

chemical elements are arranged according to increasing atomic weight, those with similar physical and chemical
properties occur after each interval of seven elements.”

TABLE6.1: Newlands’ Law of Octaves Octaves

H Li Ga B C N O

F Na Mg Al Si P S

Cl K Ca Cr Ti Mn Fe

Co, Ni Cu Zn Y In As Se

Br Rb Sr Ce, La Zr Di, Mo Ro, Ru

Pd Ag Cd U Sn Sb Te

I Cs Ba, V Ta W Nb Au

Pt, Ir Tl Pb Th Hg Bi Th

Newlands was one of the first to detect a periodic pattern in the properties of the elements and anticipated later
developments of this periodic law. However, Newlands’ table, like Meyer’s, did not gain widespread acceptance and
use, primarily because it required the omission of several known elements without any real explanation, and few
testable predictions could be made from his proposals.

Dmitri Mendeleev’s Periodic Table

At this point in history, the sharing of scientific information was not as systematic as it is today, so multiple scientists
could be working on the same ideas in different parts of the world without even realizing it. In 1869, Russian chemist
Dmitri Mendeleev (1834–1907) independently described an arrangement of about 60 elements based on increasing
atomic weight (Figure6.2).

Mendeleev’s table was similar to some of the other ones mentioned above, but it gained more widespread acceptance,
due in part to its predictions of properties for elements that were not yet known. Rather than omitting elements
where the periodic trends did not seem to fit, he left placeholders for elements that he predicted would eventually
be discovered. The predicted properties (including atomic mass, valence, and melting points) of "eka-boron", "eka-
aluminum", and "eka-silicon" were found to be very close to those of the subsequently discovered elements scandium
(1879), gallium (1875), and germanium (1886). The discoveries of these elements provided very strong evidence in
support of Mendeleev’s table, and it provided the basis for our modern periodic table of the elements.

Here is a short video describing Mendeleev’s discovery: http://www.youtube.com/watch?v=rBroXfaavw0 (4:05).

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The Modern Periodic Table

In Mendeleev’s table, atomic mass increases from top to bottom of vertical columns, with successive columns going
left to right. Elements that are in the same horizontal row are groups of elements that were known to exhibit similar