Question

Write the increasing order of reactivity of 1st group metals.

Answer 1

Hint: As the name suggests, the reactivity of metals can be determined by replacing the cation from its aqueous solution. Reactive metals are those metals which can easily lose electrons to give positive ions by reacting with some other substances.

Complete step by step answer:
As we know, the first group metals of periodic table commonly called alkali metals and these metals are Lithium (Li), Sodium (Na), Rubidium (Rb), Caesium (Cs), and Francium (Fr).
These metals are highly reactive. Alkali metals can form ionic compounds along with other compounds that are when non-metal and metal come together.
First group of metals of the periodic table have charge of +1 with largest atom sizes compared to other elements of the same period.
Therefore, the increasing order of reactivity of metals of the first group of the periodic table are as follows:
$Li < Na < K < Rb < Cs < Fr$
As we know elements of group one contain one electron in the valence shell and that is why having a strong tendency to lose valence electrons. Therefore, as we go down the group the ionization enthalpy decreases and that is why the tendency to lose valence electrons depends on the ionization enthalpy factor.

Now let us discuss ionization enthalpy in brief and why it decreases down the group?
i) Ionization energy denoted as IE is the minimum amount of energy required to remove most likely bound electrons the valence electrons of an isolated gaseous atom in its ground state.
ii) Ionization energy decreases down the group because the atomic radius increases meaning the number of shells increases and thus shielding effect decreases.
Therefore, force of attraction between nucleus and electron decreases and hence low energy is required to remove electrons from the outermost shell.
And thus reactivity of metals related to the ionization enthalpy factor or we can conclude from the above statement is that reactivity of metals inversely proportional to the ionization enthalpy which means, if ionization enthalpy of metals decreases as we move down to the first group then reactivity of metals increases.

Note: Remember, not to confuse among ionization energy and electron gain enthalpy because ionization energy is the amount of energy required to remove an electron from the outermost shell in the gaseous state whereas electron gain enthalpy is the energy released when an electron added to an isolated gaseous atom.