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

The element is beryllium ($Be$). There are no 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) $1s^22s^2$ (Look at the small numbers above the subshell to find out how many electrons it has) - Subshell $1s$: 2 electrons - Subshell $2s$: 2 electrons In total, the element has 4 electrons. 2) Since the number of electrons is equal to the atomic number of the element, the atomic number of the element is 4. 3) The element that has the atomic number 4 is beryllium ($Be$) 4) We know that subshell s has 1 orbital, so its capacity for electrons is 2 electrons at most for each s-subshell. Here, each subshell $1s$ and $2s$ already has 2 electrons, so they are paired inside the one-and-only orbital in each subshell. Therefore, there are no unpaired electrons.