Periodic Classification of Elements
NIOS · Class 10 · Science & Tech
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Development of Classification of Elements
- The first classification of elements was into metals and non-metals.
- Germanium and antimony showed properties of both metals and non-metals, so this simple classification was limited.
- William Prout’s 1815 work showed that the atomic mass of an element remains constant, which became a basis for classification.
Dobereiner’s Triads
- In 1829, J.W. Dobereiner grouped elements into sets of three called triads.
- The middle element of a triad had an atomic mass nearly equal to the arithmetic mean of the other two.
- The middle element also had properties intermediate between the other two.
Newlands’ Law of Octaves
- In 1864, John Alexander Newlands arranged elements in increasing order of atomic mass.
- He observed that every eighth element had properties similar to the first.
- This was called the Law of Octaves.
Mendeleev’s Periodic Law and Periodic Table
- D’mitri Mendeleev studied 63 known elements and their compounds.
- In 1869, he stated that the chemical and physical properties of elements are a periodic function of their atomic masses.
- He arranged elements in increasing order of atomic mass and placed elements with similar properties in the same group.
Key Concepts
Central concept: Periodic classification of elements based on atomic mass and atomic number, showing the development from early classifications to the modern periodic table
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