# Chapter 6 - Electronic Structure of Atoms - Exercises: 6.75e

The condensed electron configuration of $U$ is $$U:[Rn]5f^36d^17s^2$$

#### Work Step by Step

*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. 1) The nearest noble gas element of the lower atomic number of uranium ($U$) is radon ($Rn$). Therefore, we would use $Rn$ in the condensed electron configuration of $U$. 2) Looking at the periodic table, - $U$ is on the 7th row. The outer shell is the 7th shell. - $U$ is the sixth element in the 7th row, so it has 6 outer-shell electrons. 3) Now things become more difficult. The appearance of the f-subshell, having many more orbitals, and the great number of electrons create a very complicated situation of electron-electron repulsions, making the energy levels of the subshells become very unusual, especially with f-subshells. Normally, in this case, unless you are required to remember, you can look at the electron configuration from the periodic table: $$U:[Rn]5f^36d^17s^2$$

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