Chemistry: The Central Science (13th Edition)

The condensed electron configuration of $Cs$ is $$Cs: [Xe]6s^1$$
*Strategy: 1) Find the nearest noble gas element of the lower atomic number. 2) Find out which shell is the outer shell and how many electrons there are in the outer shell (by looking at the periodic table). 3) Put the outer-shell electron in the orbitals and subshells according to Hund's rule. Cesium ($Cs$) has 55 electrons. The nearest noble gas element of the lower atomic number is xenon ($Xe$). Therefore, we would use $Xe$ in the condensed electron configuration of $Cs$. Looking at the periodic table, - $Cs$ is on the 6th row. The outer shell is the 6th shell. - $Cs$ is on the 1st column. The number of outer-shell electron is 1. Since there is only 1 outer-shell electron, it would occupy the subshell of the lowest energy in the 6th shell, which is the s-subshell. In conclusion, the condensed electron configuration of $Cs$ is $$Cs: [Xe]6s^1$$