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Introduction to Metals and Non-Metals

Man has always been in search of order in nature. When only a few elements were known, studying them separately was not a problem. During the late eighteenth and early nineteenth centuries, as more and more elements began to be discovered, it became cumbersome to remember their characteristic properties and the compounds formed by them. Hence, it became important to classify the elements as classification would help to:
  1. Study the elements in an organised manner,
  2. Understand the relationship between the different classes of elements and
  3. Understand the gradation of properties of elements belonging to the same group.
The history of periodic table can be studied from Table.
History of Periodic Table
Scientists Basis of Classification Work
Lavoisier (1789) Defined an element. Made the first list of elements (23).
Dobereiner (1817) Similarity in chemical properties Observed a relationship between atomic weights and properties of elements. Classified three elements into each group and called them triads.
Newlands (1863) Relationship between similarity in chemical properties and atomic mass Found that elements could be arranged in the increasing order of atomic masses so that every eighth element is similar to the first. Classification is called octaves.
Mendeleef (1869) Increasing order of atomic weights Periodicity of properties noticed. Mendeleef’s periodic classification of elements.
Moseley (1912) Increasing order of atomic numbers Proposed periodicity of properties of elements as a function of their atomic number.

A tabular arrangement of elements in rows and columns which highlights the regular repetition of properties of the elements is called a periodic table. Figure 3.1 depicts the modern periodic table.
Modern periodic law: The properties of the elements are periodic functions of their atomic numbers.
Modern Periodic Table (see coloured figure on inside front cover)

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