Man's physical universe

xanabras

UNIT VIII

SECTION 3

ATOMS ARE COMPLEX AND MAY BE TRANSFORMED

BY NUCLEAR CHANGES

We find ourselves, in consequence of the progress of physical science, at

the pinnacle of one ascent of civilization, taking the first step upward out on

the lowest plane of the next. Above us rises indefinitely the ascent of physical

power — far beyond the dream of mortals in any previous system of philosophy.

— Frederick Soddy.

Introduction.

William Prout, having observed that many atomic weights are whole

numbers and having assumed that all atomic weights would prove to

be whole numbers, advanced the hypothesis that the atoms of all elements

are simple multiples of the atoms of smallest mass, those of

hydrogen. Prout was on the track of a great idea, but it was not until

some of the information presented in this Section became available

that his idea that atoms are complex in nature received confirmation.

The Periodic Law Suggests Atomic Complexity.

In 1865 John Newlands observed that the elements seem to exist as

Today, for example, we recognize that the inert gases of the

families.

atmosphere — helium, neon, argon, krypton, and xenon — are so

much alike chemically that it is difficult to separate them. These

elements had not been discovered in Newlands' time, but he observed

other families with similar characteristics. For example, the alkali

group consists of lithium, sodium, potassium, rubidium, and cesium,

all very active metals with a combining power of one. Another such

family is

the alkaline earth group, consisting of magnesium, calcium,

strontium, and barium, which are metals which pccur in similar types

of compounds and exhibit a combining power of two. The halogens are

a group of very active nonmetals with a combining power of one. This

group consists of fluorine, chlorine, bromine, and iodine. Newlands

arranged the elements in the increasing order of their atomic weights

and observed that every eighth element seemed to belong to the same

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