The valency of an element doesn’t changes while going down the group. It remains the same because the elements belongs to the same group contains same no. of valence electrons.
1) When going from left to right in a period of the periodic table, the valency increases from 1 to 4 and then it decreases from 4 to 0.
2) As we move from left to right in a period, the nuclear charge on an element increases but the number of energy shells remains the same. Due to increase in the nuclear charge, the force of attraction between nucleus and electrons increases. As a result, the size of the atom decreases on moving from left to right in a period.
3) When we move down in a group, the size of the atom increases due to introduction of a new shell of electrons at each step.
4) Metallic character decreases when we go down in a group due to decrease in the electronegativity of the elements.
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