Video Transcript
Metals are typically shiny and electrically conductive, while ionic solids are dull and electrically insulating. Which feature of metals is responsible for this difference? (A) The atomic mass of the nuclei, (B) the number of neutrons in the nuclei, (C) the crystal lattice of positive ions, (D) the delocalized electrons, or (E) the charges of the positive ions.
This question is asking us to determine the feature present in metals that give them their typical shine and electrical conductivity. We are to compare this to ionic solids, which typically do not have shine and therefore appear dull and do not conduct electricity, but rather are insulating. Let’s have a closer look at the structure of metals and ionic solids so that we can determine the feature that causes these differences.
Metals are composed of a lattice of positively charged ions and what is sometimes referred to as a sea of delocalized electrons. They are held together by the strong attraction between the positively charged ions and the negatively charged electrons. These electrons are highly mobile within the lattice. Ionic solids also have a lattice structure. However, this lattice is composed of oppositely charged ions. These ions are very strongly attracted to one another and in the solid state stay rigidly immobile within the lattice.
Let’s now have a look at the properties of shine and conductivity. Generally, for a material to shine, light must be able to be reflected on its surface. The delocalized electrons on the surface of a metal can absorb and reflect amounts of light, resulting in the typical shiny appearance of a metal. This phenomenon does not occur with ionic solids. Electrical conductivity occurs when electric charges can flow through a material. In metals, the delocalized electrons can flow easily through the lattice of positive ions. Since delocalized electrons in metals results in the flow of charge, metals are electrically conductive.
In an ionic solid, the charged ions cannot flow and are rigidly structured within the lattice. Charges are immobile in the structure of ionic solids, making them electrically insulating, not conductive. Metals are shiny and electrically conductive due to their delocalized electrons. Therefore, the feature of metals that is responsible for the difference in shine and conductivity between metals and ionic solids is answer choice (D) the delocalized electrons.
