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People Behind the Science

Dmitri Ivanovich Mendeleyev (1834–1907)

mitri Mendeleyev was a Russian He could find no textbook adequate for his
Dchemist whose name will always be students’ needs, so he decided to produce his
linked with his outstanding achievement, own. The resulting Principles of Chemistry
the development of the periodic table. He (1868–1870) won him international renown; it
was the first chemist to understand that all was translated into English in 1891 and 1897.
elements are related members of a single Before Mendeleyev produced his peri-
ordered system. He converted what had odic law, understanding of the chemical
been a highly fragmented and speculative elements had long been an elusive and
branch of chemistry into a true, logical sci- frustrating task. According to Mendeleyev,
ence. The spelling of his name has been a the properties of the elements are peri-
source of confusion for students and frus- odic functions of their atomic weights. In
tration for editors for more than a century, 1869, he stated that “the elements arranged
and the forms Mendeléeff, Mendeléev, and according to the magnitude of atomic
even Mendelejeff can all be found in print. weights show a periodic change of proper-
Mendeleyev was born in Tobol’sk, ties.” Other chemists, notably Lothar Meyer
Siberia, on February 7, 1834, the youngest of in Germany, had meanwhile come to simi- of the periodic law. Three were discovered
the 17 children of the head of the local high lar conclusions, with Meyer publishing his in Mendeleyev’s lifetime: gallium (1871),
school. His father went blind when Men- findings independently. scandium (1879), and germanium (1886),
deleyev was a child, and the family had to Mendeleyev compiled the first true all with properties that tallied closely with
rely increasingly on their mother for support. periodic table, listing all the 63 elements those he had assigned to them.
He was educated locally but could not gain then known. Not all elements would “fit” Farsighted though Mendeleyev was, he
admission to any Russian university because properly using the atomic weights of the had no notion that the periodic recurrences
of prejudice toward the supposedly backward time, so he altered indium from 76 to 114 of similar properties in the list of elements
attainments of those educated in the prov- (modern value 114.8) and beryllium from reflected anything in the structures of their
inces. In 1855, he finally qualified as a teacher 13.8 to 9.2 (modern value 9.013). In 1871, he atoms. It was not until the 1920s that it was
at the Pedagogical Institute in St. Petersburg. produced a revisionary paper showing the realized that the key parameter in the peri-
He took an advanced-degree course in chem- correct repositioning of 17 elements. odic system is not the atomic weight but the
istry. In 1859, he was sent by the govern- To make the table work, Mendeleyev atomic number of the elements—a mea-
ment for further study at the University of also had to leave gaps, and he predicted sure of the number of protons in the atom.
Heidelberg, and in 1861, he returned to St. that further elements would eventually Since then, great progress has been made in
Petersburg and became professor of general be discovered to fill them. These predic- explaining the periodic law in terms of the
chemistry at the Technical Institute in 1864. tions provided the strongest endorsement electronic structures of atoms and molecules.

Source: Modified from the Hutchinson Dictionary of Scientific Biography © Research Machines 2008. All rights reserved. Helicon Publishing is a division of Research Machines.

Elements with one, two, or three outer electrons tend to
lose electrons to form positive ions. The metals lose electrons an atomic number of 8. The square with the symbol
like this, and the metals are elements that lose electrons to form O and the atomic number 8 is located in the column
positive ions (Figure 8.20). Nonmetals, on the other hand, are identified as VIA. Since the A family number is the same
elements with five to seven outer electrons that tend to acquire as the number of electrons in the outer orbital, oxygen
has six outer orbital electrons. (b) Calcium has the
electrons to fill their outer orbitals. Nonmetals are elements that
symbol Ca (atomic number 20) and is located in column
gain electrons to form negative ions. In general, elements located
IIA, so a calcium atom has two outer orbital electrons.
in the left two-thirds or so of the periodic table are metals. The
(c) Aluminum has the symbol Al (atomic number 13) and
nonmetals are on the right side of the table (Figure 8.19).
is located in column IIIA, so an aluminum atom has three
outer orbital electrons.
CONCEPTS Applied
Outer Orbitals

How many outer orbital electrons are found in an atom The dividing line between the metals and nonmetals is a
of (a) oxygen, (b) calcium, and (c) aluminum? Write your steplike line from the left top of group IIIA down to the bot-
answers before you read the answers in the next paragraph. tom left of group VIIA. This is not a line of sharp separation
(a) According to the list of elements on the inside between the metals and nonmetals, and elements along this
back cover of this text, oxygen has the symbol O and line sometimes act as metals, sometimes as nonmetals, and
sometimes as both. These hard-to-classify elements are called

220 CHAPTER 8 Atoms and Periodic Properties 8-18