How many groups and periods are there in the modern periodic table? How do the atomic size and metallic character of elements vary as we move :

(i) down a group and (ii) from left to right in a period?

There are 18 groups and 7 periods in the modern periodic table.

(i) Atomic size and metallic character of the elements increases down a group.

Explanation- When we move from top to bottom a new shell of electrons is added to the atoms at every step. In this way number of electrons increases which increases the size of atoms.

Since one more shell is added the atom can lose the electron easily to form positive ion thus metallic character increases.

(ii) Atomic size and metallic character of elements decreases from left to right in a period.

Explanation- As we move from left to right atomic number increases i.e. number of electrons and protons in atom increases. Due to this large positive charge electrons are pulled close to the nucleus and size decreases.

Due to increased nuclear charge the valance electrons are pulled in more strongly by the nucleus and it becomes difficult for atoms to lose electrons. Hence they become less metallic.