What is the most likely reason that nonmetals are electrical insulators? since valence shells are mostly empty in nonmetal atoms, the atoms attract and hold any electrons they can in order to fill their valence shells. since valence shells in nonmetal atoms are almost full, the atoms attract electrons and hold them tightly to fill their valence shells. since all nonmetals have valence shells that are full, they hold electrons tightly to avoid changing. since all nonmetals have valence shells that are completely empty, they do not attract or release any electrons.

Since valence shells in nonmetal atoms are almost full, the atoms attract electrons and hold them tightly to fill their valence shells.

Explanation:

1) Insulating is the property of non permiting the flow of current.

2) The current is carried by electrons, so if the electrons move there is flow of current, and if the electrons do not move there is not flow of current and the material is an insulator.

3) The nonmetlas are in the righ part of the periodic table: columns 14 to 18 (but not the entire columns, column 14 has only 1 nonmetal, column 15 has two nonmetals, column 16 has 3 nonmetals, column 17 has 4 nonmetals, and column 18 has 7 nonmetals). Those elements have the valence shells almost full (which you can predict in virtue of ther positions in the periodic table) and so they are not willing to let the electrons to move freely from one atom to another, instead they prefer to keep their electrons and fill the valence shell (stable configuration).

Hence, the no flow of the electrons explains the insulating property.