Indicate whether each statement is true or false: (a) Substitutional alloys tend to be more ductile than interstitial alloys. (b) Interstitial alloys tend to form between elements with similar ionic radii.

Verified step by step guidance

1. Step 1: Understand the difference between substitutional and interstitial alloys. Substitutional alloys are formed when atoms of the solute metal replace atoms of the host metal in the lattice. Interstitial alloys are formed when smaller atoms fit into the spaces (interstices) between the larger host metal atoms.
2. Step 2: Consider the properties of substitutional alloys. These alloys tend to be more ductile because the atoms are of similar size, allowing them to slide past each other more easily under stress.
3. Step 3: Evaluate the statement (a). Since substitutional alloys are more ductile due to the similar size of the atoms, the statement 'Substitutional alloys tend to be more ductile than interstitial alloys' is true.
4. Step 4: Consider the formation of interstitial alloys. These alloys typically form when smaller atoms, such as carbon, fit into the interstices of a metal lattice, like iron in steel. The smaller atoms do not have similar ionic radii to the host metal atoms.
5. Step 5: Evaluate the statement (b). Since interstitial alloys form between elements with different ionic radii, the statement 'Interstitial alloys tend to form between elements with similar ionic radii' is false.

Key Concepts

Substitutional Alloys

Substitutional alloys are formed when atoms of one metal replace or substitute for atoms of another metal in the crystal lattice. This type of alloy typically retains the ductility of the parent metals, as the larger atoms can accommodate the smaller ones without significantly disrupting the overall structure. Common examples include brass, which is an alloy of copper and zinc.

Interstitial Alloys

Interstitial alloys are created when smaller atoms fit into the spaces (interstices) between the larger metal atoms in a crystal lattice. These alloys often exhibit increased hardness and strength but reduced ductility compared to substitutional alloys. An example is steel, where carbon atoms occupy interstitial sites in iron.

Ionic Radii and Alloy Formation

The ionic radii of elements play a crucial role in determining the type of alloy that can form. Substitutional alloys typically form between elements with similar ionic radii, allowing for effective substitution without significant lattice distortion. In contrast, interstitial alloys usually involve a significant size difference, where smaller atoms fit into the spaces of larger atoms.