Explain the modern periodic table.

Ans. 1. In 1913, Henry Moseley, an English physicist found that it was atomic number (Z) and not atomic mass which was the fundamental property of an element. Thus atomic number is useful for arrangement of elements in the periodic table.

  1. The modern periodic table is also called as long form of periodic table.

  2. In the modern periodic table, elements are arranged in the increasing order of atomic number (Z).

  3. The modern periodic table contains 7 horizontal rows called as periods and 18 vertical columns called as groups.

  4. Apart from the seven rows, there are two additional rows called lanthanide series and actinide series placed at the bottom of the periodic table.

  5. Based on electronic configuration, the modern periodic table is divided into four blocks namely, s-block, p-block, d-block and f-block.

  6. The blocks gives rise to 4 types of elements namely normal elements, zero group elements, transition elements and inner-transition elements.

  7. Elements belonging to a particular group show strong resemblance in their chemical properties like valency, formulae of compound and chemical reactions.

  8. Elements show gradual variation in chemical properties along a period.

  9. Neighbouring elements within a period show some similarities but non- neighbours show appreciable dissimilarity in their chemical properties.