Explanation:
An atom of sulfur contains 16 protons, because its atomic number is 16, and 16 electrons, in order to be net-neutral. For reasons identical to those described in the previous section, the neutron count for this particular sulfur atom is irrelevant to the analysis that will be performed in the following paragraphs and will not be discussed further.
Sulfur's electron configuration, which was first determined in Section 2.6, is shown below.
1s22s22p63s23p4
Sulfur has 6 valence electrons, as determined either by totaling the electrons found within the orbitals in the highest occupied energy level, which, in this case, includes both the 3s and 3p orbitals, or by identifying the "A/B System" group number for the column in which the element is found.
In order to be stable, a particle must possess an octet, or eight, fully-paired valence electrons. Sulfur would need to gain 2 electrons in order to achieve an octet configuration. Unlike in the calcium example presented in the previous section, gaining this number of electrons is possible, as doing so would not exceed the maximum gain-limit of three electrons. Therefore, sulfur will gain two additional valence electrons.
Consider the impact that this will have on sulfur's electron configuration. The rules presented in Section 2.6 dictate that if two additional electrons are added, they must both be placed in the 3p orbital, in order to fill that orbital to its maximum capacity.
1s22s22p63s23p(4+2)
Simplification of the 3p orbital's superscript results in a new electron configuration, as shown below.
1s22s22p63s23p6
In this new electron configuration, the number of valence electrons contained in the corresponding particle are still determined by totaling the electrons found within the the 3s and 3p orbitals.
3s23p6
The superscripts associated with these orbitals now sum to 8. Therefore, this new particle has 8 valence electrons and has achieved, through the process described above, a highly-stable octet configuration.
Note that the number of protons was unchanged in the process described above, so this new particle still contains 16 protons. Since the identity of an element is defined by the number of protons that it contains, due to the association between atomic number and proton-count, this new particle is still a form of sulfur. However, since this new particle was formed through the gain of two valence electrons, it now has 18 (16 + 2) electrons. Therefore, this new particle is no longer a sulfur (S) atom which, as stated above, contains 16 electrons.
