Question

Lithium, Sodium, and Potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity between the atoms of these elements?

Answer 1

To find any similarity between elements make sure that they are placed in the same group in the periodic table. Lithium, Sodium, and Potassium with atomic numbers 3, 11, and 19 respectively are placed in the first group in the periodic table. Elements in the same group tend to show the same properties.

Complete answer:
Lithium, Sodium, and Potassium react with water to form hydroxides or alkalis with the liberation of hydrogen gas.
Let us first see the reaction of these metals with water.
Lithium reacts with water to form Lithium hydroxide.
$2Li\text{ +}\text{ 2}{{\text{H}}_{2}}O\text{ }\to \text{ 2LiOH + }{{\text{H}}_{2}}$
Sodium reacts with water to form Sodium hydroxide which is a popular base.
$2Na\text{ +}\text{ 2}{{\text{H}}_{2}}O\text{ }\to \text{ 2NaOH + }{{\text{H}}_{2}}$
Potassium reacts with water to form Potassium hydroxide which is also a popular base.
$2K\text{ +}\text{ 2}{{\text{H}}_{2}}O\text{ }\to \text{ 2KOH + }{{\text{H}}_{2}}$
These metals react easily with water to liberate hydrogen because they have one electron in the last shell.
The similarity between Lithium, Sodium, and Potassium:
All the three elements are present in the same group so they have only one electron in the outermost shell.
These metals are highly unstable and react vigorously with water.
These elements are called alkali metals as they form alkalis with water.
The chemical reactivity of these metals is quite high.
When they lose one electron they form protons with a +1 charge.
The second ionization enthalpy of the elements is more than the first ionization enthalpy.

Note:
When these elements lose one electron they gain the electronic configuration of the nearest noble gas. $L{{i}^{+}}$ has the electronic configuration of Helium. $N{{a}^{+}}$ has the electronic configuration similar to Neon and ${{K}^{+}}$ has the electronic configuration same as Argon.