The charge on the monatomic ion formed by each of the following elements is:
a. 3Li - +1
b. 15P - -3
c. 16S - -2
d. 13Al - +3
This is because monatomic ions have a charge that corresponds to the number of valence electrons that they need to gain or lose in order to achieve a stable electron configuration. For example, lithium (Li) has one valence electron and needs to lose one electron in order to achieve a stable electron configuration, so it forms a +1 ion. Similarly, phosphorus (P) has five valence electrons and needs to gain three electrons in order to achieve a stable electron configuration, so it forms a -3 ion. Sulfur (S) has six valence electrons and needs to gain two electrons in order to achieve a stable electron configuration, so it forms a -2 ion. Finally, aluminum (Al) has three valence electrons and needs to lose three electrons in order to achieve a stable electron configuration, so it forms a +3 ion.