Man's physical universe

xanabras

UNIT VIII

SECTION 4

MOLECULES ARE HELD TOGETHER BY ELECTRICAL

OR MAGNETIC ATTRACTION OF ATOMS

Introduction.

Chemical changes represent rearrangements of atoms within molecules

or the decomposition or combination of molecules to form smaller

or larger molecules containing fewer or more atoms. What force holds

atoms together within molecules? Are these forces the same for all

atoms? By what means may these forces be overcome to bring about

new arrangements of atoms within molecules? These are the questions

which have puzzled chemists for many years. Some of them can now

be answered, although the answers are very incomplete.

Chemical Affinity Was First Used to Explain the Attraction between

Atoms.

In the thirteenth century, the Dominican monk, Alhertus Magnus,

used the word "afifinitas," which expressed the idea that only atoms

having a similarity or kinship would unite to form molecules. The

Greek philosopher, Hippocrates, expressed the same idea when he

maintained that "like unites only with like."

In the eighteenth century

Boerhaave and others arrived at the opposite conclusion, namely, that

dissimilar atoms show the greatest tendency to combine.

Before the knowledge of electricity developed, the nature of this

force of affinity was not known. The terms "love" and "hate" were

often used for want of anything better. It was known, however, that

the affinity between the various atoms differed, and many attempts

were made to arrange the elements in the order of their affinity for

other elements. Today it is believed that chemical affinity is a force,

electrical in nature, which acts between the different kinds of atoms to

bring about chemical changes.

The Properties of the Elements Depend upon Their Structures.

Some metals are good conductors of electricity; others are not.

Some metals may be pulled out to form fibers smaller in diameter than

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