Question

The number of neutral molecules or negative groups attached to the central metal atom in a complex ion is called:
(A) atomic number
(B) Effective atomic number
(C) Coordination number
(D) Primary valency

Answer 1

In order to find what are the number of neutral molecules which are attached to the central metal atom in a complex ion called, we must know about Werner's theory. From the Werner’s theory we will get primary and secondary valency.

Complete answer:
- Let us understand about Werner's theory. According to this theory, central metal atoms or ions will be having two valencies namely the primary valency and the secondary valency.
- Primary valency is based on the number of negative ions that are equivalent to the charge that is present on the metal ions. Primary valency will give the oxidation number of the central metal ion.
- Secondary valency is based on the number of the neutral molecules or negative groups which are attached to the central metal ion. These neutral molecules or negative ions are called ligands. Secondary Valency will give the coordination number of the central metal ion.
- The primary valencies are said to be ionizable quantities. The secondary valencies are said to be non-ionizable.
Therefore, the correct option is option (C).

Note: Werner’s theory has also got some limitations. It failed to explain about the
- Color
- Magnetic properties
- directional properties
- optical properties
- inability of all elements to form the coordination compounds.