The Indianapolis times. [volume] (Indianapolis [Ind.]) 1922-1965, 1924-04-09

GROUPED IN
FAMILIES
Five Substances Unknown
but Are Believed Certain
to Exist,
to Exist,
BY DAVID DIETZ
Science Editor of The Times
lCnn,rrin.ht hrr TNarid DietzA


Is HEMISTS soon began to notice
IL that certain elements re-
IL sembled certain other ones
very strongly. For example, let us
take sodium. Sodium is a soft silvery
white metallic element. When dropped
into water. it reacts violently with
the water, decomposing or breaking
up the water into its two components,
hydrogen and oxygen The sodium
unites with the oxygen and part of
the hydrogen to form a compound
known as caustic soda while the rest
Of the hydrogen is set free
Another element potassium was
found to resemble sodium very much
in appearance and to have the same
effect on water.
Sodium and potassium resemble
each other in many other ways
Sodium unites with chlorine to form
ordinary table salt. Potassium
unites with chlorine to form a SINH
lar salt called potassium chloride.
These examples of the similarity be-
a long list.
Has Same characteristics
A third element Hthium, has the
same characteristics as sodium and
potassium.
Therefore it looked to the chemist
very much as though hthium, sodium
and potassium all belong to one
family
Othor fap,iIias aIso sao,,ad to 80
list. Thus chlorine, bromine and
iodine seemed to belong to the same
family
In fact it soon became apparent to
chemists all the elements could be
grouped by families.
Atoms of different elements. as
the reader now knows. have different
weights.
The chemist therefore set TO de-
termine the relative weights Of differ
ent atoms. Oxygen was taken as the |
standard and assigned a weight Of
sixteen. The atomic weight Of other
elements was expressed by compar-
Ing the weight of their atoms to that
of the oxygen atom.
Z on this basis, the atomic weight Of
hydrogen is zoos, Of helium 3.89. Of
Iithlum. 6.94 and so on
Relationship Interesting
Now an interesting relationship was
noticed when the elements were ar
ranged in order according to their
atomic weights.
II appeared that with certain excep- /
tons every eighth element in the ser
les resembled each other. For ex-
ample if we took lithium and counted
down eight we would come to sodium. /
Counting eight from sodium would
bring us TO potassium
A Russian chemist. Professor Dmi- /
tn Mendeleef was the first to recog- 1
nize the full significance of this. Ac- /
cordingly he arranged all the elements /
by families in a table which is known |
to chemists as the periodic table.
At the time he did this there were 1
only some eighty elements known. Ac- /
oordingly he left blank spaces in his /
table where there was no element to /
At in.
Predicted Discovery
So confident was he in his table, |
that he predicted that the missing ele-
ments would be eventually discovered /
and that when discovered they would !
have the atomic weights and proper |
ties which the blank spaces in his |
table indicated they ought to have.
Since Mendeleef's day some of these !
elements have been found and his |
predictions as to their atomic weight |
and characteristics have proved true. |
We said there are ninety-two ele- |
ments. AS a matter Of fact there are .
only eighty-seven known elements to-
day. But the chemist still has faith |
in Mendeleef's table and feels certain |
that the other five elements exist al.
though he hasn't found them yet.
There were six missing elements |
until 1928 when the element hafnium |
was discovered
Next article in series: Atomic Num-
bers.