A Historic Overview: Mendeleev And The Periodic Table

Mendeleev continued laying down his cards and felt comfortable identifying two more gaps or “missing” elements in the

fourth column, in the third and fourth rows. His genius is shown in his ability to recognize the potential for missing data

and to use existing data to predict the properties of these unknown elements. Mendeleev left spaces on his periodic

tables because he did not "force" the known elements to fit any preconceived pattern. The absence of elements with

certain physical and chemical properties also indicated that not all existing elements had yet been discovered.

Mendeleev interpolated from what he knew to make predictions about what was missing. These predictions guided the

search for other elements.

Mendeleev not only suggested that elements similar to aluminum and silicon should exist. He predicted several

properties of "ekasilicon". “Eka” means “first,” “beyond,” or “after” in Greek.

Mendeleev thought ekasilicon would have a specific gravity of 5.5, and its oxide would have a specific gravity of 4.7. He

was right on both counts. These values are close to those eventually found for germanium. Gallium (similar to aluminum)

and germanium (similar to silicon) were discovered in 1871 and 1886, respectively.

Prediction of Properties of an Unknown Element

Ekasilicon

Germanium

Atomic weight

72.32

Specific gravity

5.5

5.47

Color

dark grey

greyish-white

Formula of oxide

EsO 2

GeO 2

Specific gravity of oxide

4.7

4.70

Formula of chloride

EsCl 4

GeCl 4

Specific gravity of chloride

1.9

1.887

Boiling point of chloride

below 100°C

83°C

Mendeleev focused on the chemical properties of the elements. He concluded that certain commonly accepted values

for atomic masses were incorrect. He calculated that the atomic mass of chromium would be greater than the value

being used at that time. Although there was a place in the table for chromium between calcium and titanium based on

the incorrect value for its atomic weight, the properties of chromium did not fit with this placement.

By 18 71 , M en de le e v ha d m od if i ed a n d im pr o ve d his f ir st pe r io di c tab le of t he el em e nt s. He use d it s or g an i za ti on of

i nf or m a t io n to pr ed i ct t h e exist en ce of t en el em e nt s ( n o w kn o wn a s Sc, G a, G e, T c, R e, Po, F r , Ac, and Pa) . He fu ll y

d escr ib e d in gr ea t det ai l f ou r of th e se ( Sc, G a, G e, a nd Po) . H e d id th is b y i nt e r p ol at i ng i n fo r m at i on f r om w ha t w as kn ow n.

Mendeleev became world famous because of his development of the periodic table of the

101

258

elements. He traveled throughout Europe, visiting with other famous scientists. However,

Mendeleev was a political liberal. Czar Alexander II, who ruled Russia in the late 1800s, did

not approve of Mendeleev. Therefore, Mendeleev was never recognized by being elected

to the Russian Academy of Sciences. However, Mendeleev was honored posthumously in

1955 when Mendelevium, manmade element number 101 in the modern periodic table, was

named for him.

Mendelevium

Conclusion

The periodic table that hangs in many classrooms and laboratories today has a 130 year history. It is the family tree of

the elements. Although Dimitri Mendeleev's periodic table is certainly not the only chart that organizes elements based

on their properties, his table was the first to illustrate the periodic relationship between chemical groups. This table is a

tool that furthers understanding of the chemistry of the elements. From Mendeleev's Periodic Law and his determination

to find some order to the characteristics of the elements, scientists have been able to proceed with their scientific

inquiries in a logical and systematic manner.

G E N E S I S

A Historic Overview: Mendeleev And The Periodic Table - Genesis Page 4

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