Page 2 - 3. Lesson Notes Ch-5 MENDELEEVES CLASSIFICATION

 The formulae of the hydrides and oxides formed by an element were
treated as one of the basic properties of an element for its classification.

 He selected hydrogen and oxygen as they are very reactive and formed
compounds with most elements.

 So, to understand the chemical properties of elements, he took into
consideration-

Two general formulae;
a. one for oxides of elements.
b. second for hydrides of elements.

For example:
- R2O for oxides and RH for hydrides, of the elements; of 1st group.
- RO for oxides and RH2 for hydrides, of the elements; of 2nd group.

Using the given general formulae; the formula of oxides and hydrides can be
written for the elements of each group.

For example-
hydrogen, sodium, potassium, etc. belong to the first group.
The general formula of oxides for the elements of 1st group is R2O.
Accordingly they form H2O, Na2O, K2O, etc.

 He then took 63 cards and on each card he wrote down the properties of
one element.

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