# Ceramics Engineering Questions and Answers – Pauling’s Rules

This set of Ceramics Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Pauling’s Rules”.

1. What does having a high coordination number imply according to Pauling’s rule?
a) High stability
b) Low stability
c) High conductivity
d) Low conductivity

Explanation: Coordination number means number of nearest neighbors surrounding an atom. If there are more number of atoms surrounding an atom, that means it is shielded by those atoms and has low reactivity. Thus high coordination number suggests high stability.

2. Pauling’s rule’s idea is that ion of opposite sign pack together in such a way _________
a) To increase the melting point
b) To keep ions of like sign apart
c) To decrease the melting point
d) To keep ions of opposite sign apart

Explanation: According to Pauling’s rule, atoms and molecules should attain stability. If ions of same sign are packed together, there will be a force of repulsion. To avoid this, ions of opposite sign should pack together.

3. According to Pauling’s rule, how is coordination number of an atom in a molecule determined?
a) Atomic ratio
b) Molecular weight
d) Electronic ratio

Explanation: Pauling’s rule provides a standard chart of radius ratio which determines coordination number of the atoms by knowing the radius ratio of cation to anion. For instance, radius ratio between 0.414 and 0.732 shows octahedral type of void and 6 coordination number.

4. In a stable crystal, the total strength of bonds between cations and anions should be equal to ______
a) Gibbs Free Energy
b) Charge of cation
c) Internal energy
d) Charge of anion

Explanation: The given statement is Pauling’s second rule. It describes the strength of bonds between atoms and molecules. The fundamental idea is that the crystal should be electrically neutral.

5. The polyhedral in a structure tend not to share edges or faces.
a) True
b) False

Explanation: If the edges are shared, the shared edges get shortened. Shared faces are also not favorable and lead to instability. Therefore, the polyhedral in a structure tend not to share edges or faces.

6. What is the bond strength of a silicon cation in silica?
a) 0
b) 1
c) 1.5
d) 0.2

Explanation: By formula, S = $$\frac{Z_r}{CN}$$ where CN is coordination number. Charge and coordination of silicon is 4. S=($$\frac{4}{4}$$) = 1.

7. What is the bond strength of aluminium cation in alumina?
a) 0
b) 1
c) 1.5
d) 0.5

Explanation: By formula, S = $$\frac{Z_r}{CN}$$ where CN is coordination number. Charge and coordination of aluminium is 3 and 6 respectively. S=($$\frac{3}{6}$$) = 0.5.

8. Pauling’s rules are applicable to which type of structures?
a) Ionic bonded structures
b) Covalently bonded structures
c) Metallic bonded structures
d) FCC

Explanation: Pauling’s rules are applicable to structures where ionic bonding predominates. Pauling’s rules gives idea about the structure, coordination and type of voids only in ionic solids by knowing the radius ratio of the atoms. It does not give any information about covalent and metallic bonding.

Sanfoundry Global Education & Learning Series – Ceramics Engineering.