Answer
[Kr]5s$^2$4d$^1$
Yttrium has one unpaired electron.
Work Step by Step
*Strategy:
1) Find the nearest noble gas element of the lowest 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 Y is Kr. Therefore, we would use Kr in the condensed electron configuration of Y.
2) Looking at the periodic table,
- Y is on the 5th row, so the outer shell is the 5th shell.
- The atomic number of Y is 39, so the element has 39 electrons. The inner-shell electrons are 36 (the number of electrons in the first three shells). So, there are 39−36=3 outer-shell electrons.
3) Procedure:
- The s-subshell of the 5th shell is occupied first (5s$^2$)
- The last 1 electron occupies the orbitals in the 4d subshell (4d$^1$)
In conclusion, the condensed electron configuration of Y is
Y:[Kr]5s$^2$4d$^1$
4) Here we notice that all inner-shell electrons and the electrons in the 5s subshell are paired.
Therefore there is one unpaired electron.
