Question

Following statements regarding the periodic trends of chemical reactivity of alkali metals and the halogens are given. Which of these statements give the correct picture?
A) In alkali metals, the reactivity increases but for halogens it decreases with an increase in atomic number down the group.
B) The reactivity decreases in the alkali metals but increases in the halogens with an increase in atomic number down the group.
C) In both the alkali metals and the halogen, the chemical reactivity decreases with an increase in atomic number down the group.
D) Chemical reactivity increases with an increase in atomic number down the group.

Answer 1

Hint: Alkali metals are the elements present in group 1 of the periodic table. Halogens are the elements that are present in group 17 of the periodic table. One can analyze the given options and relate the given properties with the alkali metals and choose the correct option.

Complete step by step answer:
1) First of all we will learn the concepts given in the question and relate them with the statements given in the options. As we know the alkali metals are electropositive and have a metallic character.
2) The alkali metals have very low ionization energies that mean the alkali metals have a very strong tendency to lose the one valence electron to form a positive cation. Hence, these elements have a very strong electropositive or metallic character. In alkali metals the tendency to lose an electron increases when going down the group.
3) Now let us talk about the halogens which have maximum chemical reactivity that is shown by the gain of an electron forming an anion. In halogens, the tendency is to gain an electron which is highest at the top and falls down the group.
Therefore, after analyzing the given statements we can say that in alkali metals the reactivity increases but for halogens, it decreases with an increase in atomic number down the group which shows option A as the correct choice.

Note: In the halogen group when we go down the group there is a decrease in electronegativity which also decreases the reactivity. An increase in atomic size will also decrease the ability to gain electrons but it will increase the ability to donate the electrons.