EVERYDAY SCIENCE

Detailed explanation-1: -The valency of an element is determined by the number of valence electrons present in the outermost shell of an atom. The electronic configuration of the outermost shell is same for all the elements belonging to the same group. So, the number of valence electrons for all the elements in a group is the same.

Detailed explanation-2: -The elements in each group have the same number of electrons in the outer orbital. Those outer electrons are also called valence electrons. They are the electrons involved in chemical bonds with other elements. Every element in the first column i.e. group one has one electron in its outer shell.

Detailed explanation-3: -Elements in same group show same valency because they have same number of electrons in the outermost shell i.e. Valence shell. Since valency depends upon the valence electrons so they have same valency.

Detailed explanation-4: -Atoms which are present in the same group of the periodic table will have same number of valence electrons. Hence Cl, I of group 17, Na, Ca group 1 and C, Ge group 14 have same valence electrons.