Write the number of periods the Modem Periodic Table has. State the changes in valency and metallic character of elements as we move from left to right in a period. Also state the changes, if any, in the valency and atomic size of elements as we move down a group.

Number of periods in the modern periodic table is 7.

• On moving from left to right in the periodic table the valency of the elements first increases from 1 to 4 and then decreases to zero.

Explanation- For example considering the third period elements-

• On moving from left to right in a period, the metallic character of elements decreases.

Explanation- because due to increase in charge the valance electrons are pulled more strongly by nucleus and it becomes difficult to lose electrons.

• All the elements in a group have the same valency.

For example-

Thus the valency or number of valance electrons remains same down a group.

• On going down in a group, the atomic size increases

Explanation- Increase in size is because a new shell of electrons is added to the atoms at every step.