Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

CHAPTER I.

The Elements

THE PERIODIC CLASSIFICATION OF THE ELEMENTS.

THE periodic recurrence of properties among the elements has

been of the greatest service to the practical chemist in classifying

the elements. From the very outset scientists recognized that

this periodicity indicated that all elements were built up according

to some definite plan out of some primordial material. Advances

in knowledge during the past few decades have not, it is true,

revealed the ultimate nature of this primordial material, but they

have indicated very clearly some features of the systematic scheme

according to which atoms of the different elements are built from

electrons and protons, the atoms of negative and positive electricity.

The periodic classification of the elements becomes much more

enlightening when it is arranged in accordance with our present

ideas of the structure of the atom. In the following chart the

number accompanying each element is the atomic number. This

is approximately the serial number when the elements are arranged

in the order of their atomic weights, but its deeper significance is

that it represents the number of unit positive charges of the

nucleus of the atom.

We will outline briefly the modern conception of the structure
of the atom: Electricity, like matter, is atomic in nature and

consists of two kinds of atoms, -protons which are probably identical

with the hydrogen ion (they have the mass of the hydrogen atom

and the unit positive charge of the hydrogen ion) and electrons which

are of insignificant mass f r^jc that of the hydrogen atom ) and

have an equal but opposite charge to that of the hydrogen ion.

The nuclei of atoms consist of aggregates of protons and elec-

trons (except the nucleus of hydrogen which consists of a single

proton), with the number of protons in excess of the number of

electrons so that the net charge is always positive and an even

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