1.1 What is Chemistry?

http://www.ck12.org Chapter 6. The Periodic Table

Atomic Mass and Periodic Properties

One of the major developments that allowed for what became known as the periodic table was the discovery and
measurements of atomic masses. With this discovery, some characteristic properties of the elements could be related
to their relative atomic mass. This method for arranging the elements began in the early 1800s when John Dalton
(1766–1844) described elements and compounds in terms of relative weights. Using the knowledge available at the
time, Dalton prepared an early version of what later became the periodic table (Figure6.1).

FIGURE 6.1

Dalton’s Table of the Elements

Following Dalton’s work, scientists began relating chemical properties to atomic weight. This resulted in several
major discoveries, which led to the development of what we now know as the modern periodic table.

Other Early Attempts at a Periodic Table

Following the work of Dalton, a German scientist by the name of Julius Lothar Meyer (1830–1895) created a table
of elements that was organized based on the concept of valency, which has to do with the ratios in which one element
combines with another to make a compound.

Meyer published a textbook in 1864 where he presented his table of elements. Meyer’s table showed 28 elements
systematically arranged by valence into vertical columns. The atomic weights of these elements increase by similar
amounts when going stepwise from left to right across the table. There were, however, some major shortcomings of
Meyer’s table. Only a fraction of the known elements could be easily categorized by valence, due to the fact that
many elements can combine with one another in multiple different ratios (thus creating multiple different chemical
compounds).

Shortly after this, in 1865, a similar periodic table was published by English chemist William Odling (1829–1921).
Odling’s table described a systematic arrangement of 45 elements. However, some elements were omitted without
any reasonable explanation, and this version of the periodic table was quickly replaced by subsequent versions.

The Law of Octaves

Also in 1865, an English chemist by the name of John Newlands (1837–1898) published another version of the
periodic table (Table6.1). The arrangement was based on his proposed Law of Octaves, which stated that “if the