## Chemistry: The Central Science (13th Edition)

The element of the mentioned electron configuration is oxygen ($O$) and there are 2 unpaired electrons.
*Strategy: 1) Find out the number of electrons it has by summing all the electrons in different subshells. 2) The number of electrons will be equal to the atomic number of the element. 3) Look up the periodic table to find out which element it is. 1) $1s^22s^22p^4$ - Subshell $1s$: 2 electrons - Subshell $2s$: 2 electrons - Subshell $2p$: 4 electrons In total, the element has 8 electrons. 2) Since the number of electrons is equal to the atomic number of the element, the atomic number of the element is 8. 3) The element that has the atomic number 8 is oxygen ($O$). 4) We know that subshell s has 1 orbital, so its capacity for electrons is 2 electrons at most for each s-subshell. So, both s-subshells here reach their capacity, and their electrons are paired in the orbitals. P-subshell has 3 orbitals, each can carry 2 electrons in maximum. Here there are 4 electrons that need to occupy. According to Hund's rule, the first 3 electrons would occupy 3 different orbitals, then the last one would have no choice but occupy an orbital that already has 1 electron (since p-subshell has only 3 orbitals). In other words, there is 1 two-electron orbital, and 2 one-electron orbitals. That means there are 2 unpaired electrons.