Activity 1.4

How are isotopes of different elements placed in the Modern Periodic Table?

Ans:	All isotopes of the same element have same atomic number but different atomic mass. As the modern periodic table is based on atomic numbers, all isotopes of the same element are placed in the same position.

What should be the position of hydrogen in the Modern Periodic Table? Why?

Ans:

In the Modern Periodic Table, the position of hydrogen should be in group 1. Hydrogen easily donates one electron and forms a stable cation (H+). But it does not easily form a stable anion (H-, hydride anion). Hence, hydrogen should be placed in group 1 of the modern periodic table. As seen above compounds of hydrogen and compounds of sodium with halogen, sulphur and oxygen have similar formulae. This is because the electronic configuration of hydrogen resembles that of alkali metals.

Write the name, symbol and electronic configuration of first ten elements.

Ans:	Name Symbol Number of electrons Electronic Configuration Hydrogen Helium Lithium Berylium Boron Carbon Nitrogen Oxygen Fluorine Neon H He Li Be B C N O F Ne 1 2 3 4 5 6 7 8 9 10 1 2 2, 1 2, 2 2, 3 2, 4 2, 5 2, 6 2, 7 2, 8