anions
Anions form when an atom gains electrons. Nonmetallic atoms typically gain enough electrons to obtain the same electron configuration as the nearest noble gas. All the elements in Group 17 have seven valence electrons, which are arranged into an outer configuration of n s 2 n p 5 . To achieve a noble gas configuration n s 2 n p 6 , each of these elements needs to gain just one electron, resulting in an anion with a 1 charge. Similarly, Group 16 elements can obtain an n s 2 n p 6 valence configuration by forming ions with a 2 charge, and the Group 15 nonmetals will form ions with a 3 charge. Naming anions is slightly different than naming cations. The end of the elements name is dropped and replaced with the ide suffix. For example, when the chlorine atom Cl gains one electron, it becomes the chloride ion Cl - . This structure has the same electron configuration as the noble gas argon. Similarly, sulfur can gain two electrons to become the sulfide ion S 2- , which also has a noble gas configuration.