Question

The maximum covalency for representative elements is equal to (excluding 1st and 2nd period):

• A. the number of unpaired p-electrons
• B. the number of paired d-electrons
• C. the number of unpaired s and p-electrons
• D. the actual number of s and p-electrons in the outermost shell.

Answer 1

Answer: (D)

the actual number of s and p-electrons in the outermost shell.

Answer 2

For representative elements in the 3rd period and beyond, vacant d-orbitals are available. This allows the central atom to promote its valence electrons to these d-orbitals, increasing the number of unpaired electrons available for bonding. The maximum covalency is achieved when all valence s and p electrons participate in bonding, which corresponds to the total number of s and p electrons in the outermost shell (i.e., the group number for groups 13-17). For example, Phosphorus (Group 15) has 5 valence electrons ($3s^2 3p^3$) and can form $PCl_5$ (covalency 5). Sulfur (Group 16) has 6 valence electrons ($3s^2 3p^4$) and can form $SF_6$ (covalency 6). Iodine (Group 17) has 7 valence electrons ($5s^2 5p^5$) and can form $IF_7$ (covalency 7).