Question

Write a short note on metal excess and metal deficient defects.

Answer 1

To know about the defects in metals we have to know about the ions and the ions may be of three types like the ions which are positively charged are known as cations and ions which carries negative charge are anions and the ions which have no charge are neutral in nature.

Complete answer:
Metal excess defect: This defect arises due to the presence of extra cations at interstitial sites or due to the absence of anions. There are generally two types of metal excess defect first one is due to anionic vacancies which can be explained as a negative ion may be missing from its lattice site and it left a hole there which is occupied by an electron to maintain its electrical neutrality. Another effect is due to the presence of extra cation i.e. some extra cations are present at the interstitial sites and the electrons at another interstitial site maintain electrical neutrality.
Metal deficiency defects: This type of defect arises when the metal shows variable valency and this defect is also of two types. Due to cation vacancies in this defect a positive ion will be missing from its lattice site and the extra negative charge balances by acquiring two positive charges instead of one. Another effect is due to the presence of extra anion in this defect extra anions are present at the interstitial sites and the adjacent ions at another interstitial site maintain electrical neutrality.
Hence in this we can explain metal excess and metal deficiency defects.

Note:
Valency can be defined as the combining capacity of an atom and in also be defined as the number of bonds that an atom can form as part of a compound is expressed as the valency of that element and valence electrons are the electrons that are present in the outermost orbital of the atom.