There are 7 periods
the valency remains same in a group but increases by 1 unit in period
the valence electron remains same in a group but increases by i unit in peroid till 14th group and then decreases by  1 unit and reachs till zero
the no of valence shell increases in a group but remains same in a period the atomic size increases in a group because because no of shells also increases
atomic size decreases in a period as we move from left to right because due to the increase in the nuclear charge it tends to pull the outermost shell towards it which results in the contraction of the size of the atom
the metallic property increases in a group because it can easily loose the electrons because of its increased atomic size
metallic property decreases in a period because it very hard to loose the electrons as the atomic size deceases
the electro negativity increases in a period but decreases in a group
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