Question

Predict the atomic number of the next alkali metal after francium, and give its ground state electronic configuration.

Short answer

The atomic number of the element after the francium is 119.

Step-by-step solution

Electronic configuration of francium.

The atomic number of Francium is 87.

The electronic configuration of Francium is

${\text{1s}}^{\text{2}}{\text{2s}}^2{\text{2p}}^6{\text{3s}}^2{\text{3p}}^6{\text{4s}}^2{\text{3d}}^{10}{\text{4p}}^6{\text{5s}}^2{\text{4d}}^{10}{\text{5p}}^6{\text{6s}}^2{\text{4f}}^{14}{\text{5d}}^{10}{\text{6p}}^6{\text{7s}}^1$

Noble gas configuration of Francium:- .

$\left[\text{Rn}\right]{\text{7s}}^{\text{1}}$

Determining the electronic configuration of the alkali element after francium.

Alkali metals have 1 electron in the valence shell. The electronic configuration of the valence shell is given by $n{s}^1$.

Element 118 is the last element of the periodic table belonging to group 18 (noble gases) with an electronic configuration of $\left[\text{Rn}\right]{\text{5f}}^{\text{14}}{\text{6d}}^{\text{10}}{\text{7s}}^{\text{2}}{\text{7p}}^{\text{6}}$.

Since element with atomic number 118 is a noble gas, following the trends in the periodic table, the next element should have atomic number 119. The element with atomic number 119 will have one more electron than element with atomic number 118.

Therefore the next alkali metal after Francium will have atomic number 119 and electronic configuration is :

${\text{1s}}^{\text{2}}{\text{2s}}^2{\text{2p}}^6{\text{3s}}^2{\text{3p}}^6{\text{4s}}^2{\text{3d}}^{10}{\text{4p}}^6{\text{5s}}^2{\text{4d}}^{10}{\text{5p}}^6{\text{6s}}^2{\text{4f}}^{14}{\text{5d}}^{10}{\text{6p}}^6{\text{7s}}^1{\text{5f}}^{\text{14}}{\text{6d}}^{\text{10}}{\text{7s}}^{\text{2}}{\text{7p}}^{\text{6}}{\text{8s}}^1$

The noble gas electronic configuration is

$\left[\text{Og}\right]{\text{8s}}^{\text{1}}$