Periodic table cbse 10.

Classification of some elements.

1. PERIODIC CLASSIFICATION OF ELEMENTS Doberiners Traids (1875) Elements with similar properties were arranged into of three elements called traids . He could identify only three traids from the element known. 2. Newlands’ law of octaves(1866). Elements were arranged in the order of increasing atomic masses such that properties of eight elements was the repetation of the properties of first element. This law worked well with lighter elements only.

2. 3. Mendeleev’s periodic Table (1869) state that the properties of element are the periodic function of their atomic masses. Achievements Accommodated nobel gases which were discovered late. Some gaps were left to accommodate elements to be discovered later. Limitations. Could not assign a correct position to hydrogen Position of isotopes could not be explained. Wrong order of atomic masses of some elements could not be explained.

3. 4. Henry Moseley(1913). showed that anomalies in arrangement of elements could be removed when the elements were arrangement in order of increasing atomic number. Characteristics of modern periodic table. States that the properties of elements are periodic function of their atomic number. Consists of 18 vertical columns called group. Consists of 7 horizontal rows called periods. Atoms of different elements with same number of occupied outer shells are placed in same period. Position of an elements tell us about its chemical properties.

4. Trends in M odern P eriodic T able Across the period. Down the group . Atomic size Valency Metallic character or electro positive radical Non metallic character or electronegative radical Decreases First increase from 1 to 4 and then decrease to 0. decrease Increases Increases Remain same. Increases Decreases