Properties Of Interstitial Compounds - Chemistry

Several interstitial compounds are formed by the transition metals. Transition metals react with elements such as hydrogen, nitrogen, carbon, boron, etc. to form interstitial compounds. As vacant spaces of the transition metals are filled up by small atoms, these compounds are hard and rigid. The chemical properties of the parent transition metals are not altered during the formation of interstitial compounds. However, there are various changes in the physical properties such as density, rigidity, hardness, malleability, ductility, electrical conductivity, etc. steel and cast iron are the interstitial compounds of iron which are formed with carbon. In the formation of these compounds, the malleability and ductility of iron are lost to a great extent, but the tenacity of the metal increases.

Transition metals have crystals that are either hexagonal close-packed or face-centered cubic structures. Both of these lattices are very similar and have two types of holes. Firstly, there can be two tetrahedral holes per metal atom which means there is a hole between four metal atoms. Secondly, there can be one octahedral hole per atom, that is the hole is between six metal atoms. These compounds have very high melting points, higher than that of the parent transition metals.

Properties Of Interstitial Compounds

Interstitial compounds are those that are formed when small atoms like H, C, or N are trapped inside the crystal lattices of metals. They are usually non-stoichiometric and are neither typically ionic nor covalent, for example, TiC, Mn₄N, Fe₃H, VH_0.56 TiH_1.7, etc. The formulas quoted do not, of course, correspond to any normal oxidation state of the metal. Because of the nature of their composition, these compounds are referred to as interstitial compounds. The principal physical and chemical characteristics of these compounds are as follows:
(i) They have high melting points, higher than those of pure metals.
(ii) They are very hard, some borides approach diamonds in hardness.
(iii) They retain metallic conductivity.
(iv) They are chemically inert.

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Some Solved Examples

Q.1 The statement that is INCORRECT about the interstitial compound is:

(1) They are chemically reactive

(2) they are very hard

(3) they have metallic conductivity

(4) they have a high melting point

Solution:

As we learned -

The interstitial compound of transition metals

Compounds that are formed when small atoms like H, C, and N, etc are trapped inside the crystal lattices of metals called interstitial compounds

These compounds are very hard

These compounds are chemically inert

They have a high melting point, higher than that of the parent transition metals.

Incorrect option:- Interstitial compounds are very reactive.

Hence, the answer is the option (1).

.2 The major components of "Gun Metal" are"

(1) Al, Cu, Mg and Mn

(2) Cu, Zn and Ni

(3) Cu, Ni and Fe

(4) Cu, Sn and Zn

Solution:

As we learned -

"Gunmetal" is an alloy of copper with tin and zinc.

$\mathrm{Cu} 87 \%, \mathrm{Sn} 10 \%, \mathrm{Zn} 3 \%$

It is used in machine parts, guns

Hence, the answer is the option (4).

Q.3 The incorrect statement among the following is :

1)$\mathrm{RuO}_4$ is an oxidizing agent

2)$\mathrm{Cr}_2 \mathrm{O}_3$ is an amphoteric oxide

3) (correct)Red color of ruby is due to the presence of $\mathrm{Co}^{3+}$,Ṁ

4)$\mathrm{VOSO}_4$ is a reducing agent

Solution

The red color of Ruby is due to the presence of $\mathrm{Cr}^{3+}$ and not $\mathrm{Co}^{3+}$.

$\mathrm{RuO}_4$ is an oxidizing agent due to the +8 oxidation state of Ru.

$\mathrm{Cr}_2 \mathrm{O}_3$ is an amphoteric oxide, CrO is a basic oxide, and CrO₃ is an acidic oxide.

$\mathrm{VOSO}_4$ is a reducing agent.

The incorrect statement is given in Option (3).

Hence, the correct answer is the option (3).

Conclusion

Interstitial compounds/alloys are substances that are formed when a small atom like carbon, hydrogen, boron, or nitrogen can occupy space in their lattice. The conductivity exhibited by them is similar to their parent metal. These compounds are very hard. The hardness of some borides is comparable to that of a diamond. These compounds are chemically inert. Their densities are less than the parent metal. These compounds are hard and inflexible because the transition metal’s empty areas are filled with tiny atoms. During the synthesis of interstitial compounds, the chemical characteristics of the parent transition metal remain unchanged.