Question

Lithium, sodium and potassium react with water and liberate hydrogen gas. What is the similarity in these elements?

Answer 1

Step-1: Introduction

The elements in periodic table are placed in periods and groups. Groups are vertical columns in periodic table.

Lithium ($\mathrm{Li}$), Sodium ($\mathrm{Na}$) and Potassium ($\mathrm{K}$) belongs to same group 1. They all have one electron in the valence shell and have similar chemical property.

Step-2: Reaction with water

Lithium, Sodium, and Potassium react with water to give the respective hydroxides with the liberation of Hydrogen gas (${\mathrm{H}}_2$).

$$\begin{gathered} 2\mathrm{Li}+2{\mathrm{H}}_2\mathrm{O}\to 2\mathrm{LiOH}+{\mathrm{H}}_2\uparrow \\ 2\mathrm{Na}+2{\mathrm{H}}_2\mathrm{O}\to 2\mathrm{NaOH}+{\mathrm{H}}_2\uparrow \\ 2\mathrm{K}+2{\mathrm{H}}_2\mathrm{O}\to 2\mathrm{KOH}+{\mathrm{H}}_2\uparrow \end{gathered}$$

Step-3: Nature of reactivity

The reactivity of elements with water increases down the group due to the larger size of the atom.

The similarity in these elements are they have same number of valence electrons in the outermost shell. But they have different shell notations.

Step-4: Configuration of elements

The electronic configuration of Lithium is 2,1.

The electronic configuration of Sodium is 2, 8, 1.

The electronic configuration of Potassium is 2, 8, 8, 1.

Step-5: Final answer

Therefore, Lithium, Sodium and Potassium have same number of valence electrons.