Explanation:
Elements which belong to same period show similar chemical properties.
This is because elements that lie in the same group have same number of valence electrons. Hence, they tend to show same type of reactivity which makes them exhibit similar chemical properties.
For example, F, Cl, Br and I are all members of group 17 and all of the contains 7 valence electrons.
Hence, they show similar chemical properties.
Thus, we can conclude that atoms of elements in the same group have the same valence electrons.
