Write the number of periods the modern 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.

Explanation

No. of periods : 7.
Valency across a period increases from 1 to 4, then decreases from 4 to zero.
Metallic character of elements across a period decreases.
Valency remains the same down a group
Atomic size of elements increases down a group.