Question

Make a brief note of the Metal excess and Deficiency defects.

Answer 1

Metal excess defect:

1. It is a type of defect which occurs due to the presence of extra cations at the interstitial sites in a compound.
2. When an anion is missing from a lattice position in a combination with extra metal ions, it generates a void that is inhabited by an electron. Alkali metal halides, such as NaCl, KCl, and LiCl, exhibit this type of defect.

Metal excess defect types:

1. An anionic vacancy: Occurs when a negative ion is absent from its lattice position, leaving a hole that an electron fills to maintain electrical neutrality.
2. Extra cations are present at interstitial sites, and electrons at another interstitial site preserve electrical neutrality due to the existence of extra cations.
   Zinc oxide, for example, is white at ambient temperature but turns yellow when it loses oxygen when heated too much.

Metal deficiency defect

1. It is a type of defect which occurs due to the absence of cations from the lattice site.
2. The defect occurs when the metal has variable valency.

Metal deficiency defect types:

There are two types:-

1. Because of cation vacancies: When a positive ion is missing from its lattice site, the extra negative charge balances by acquiring two positive charges instead of one. This type of defect is common in compounds with variable oxidation states. Examples include ferrous oxide and nickel oxide.
2. Extra anions are present at the interstitial sites, and the adjacent ions at another interstitial site maintain electrical neutrality. This type of defect is only found in a few instances.