Why do elements in the same group have similar physical and chemical properties?
Elements in the same group have similar physical and chemical properties because they possess similar valence shell electronic configurations. This means they have the same number of electrons in the outer orbitals.
For example, all Group 1 elements (alkali metals) share the valence shell electronic configuration. Because their outermost electron arrangement is identical, they exhibit similar chemical and physical behaviors.
Thus, the properties of an element show a periodic dependence upon its atomic number, leading to the recurrence of similar properties among elements placed in the same vertical column of the Periodic Table.
Explanation
The textbook explains that elements in the same vertical column or group have similar valence shell electronic configurations and the same number of electrons in the outer orbitals. This identical outer electron arrangement is the fundamental reason for their similar physical and chemical properties, as illustrated by the Group 1 alkali metals which all have an configuration.