The vertical columns of periodic table is called group and the horizontal rows of periodic table is called periods.
The valance electron of all elements in the same group are the same but in periods the valance electron of elements in the same period increases from left to righr.
The size of atoms increases top to bottom. but in case of periods the size of atoms decreases from left to right.
Metalic reactivity increases and non metalic reactivity decreases from top to bottom. but in periods metalic reactivity decreases and non metalic reactivity increases from left to right.
