How to calculate valency of an element when atomic no is greater than 20
The Correct Answer and Explanation is:
Valency of Elements with Atomic Number Greater Than 20
To calculate the valency of an element with atomic number greater than 20, one must understand the distribution of electrons in different shells and subshells (electron configuration) and determine how many electrons the atom tends to lose, gain, or share to achieve a stable configuration, typically similar to the nearest noble gas.
Step-by-Step Calculation:
- Write the electron configuration of the element using the Aufbau principle.
- Identify the outermost shell (valence shell) — this includes the highest principal quantum number (n).
- Determine the number of valence electrons in this outermost shell.
- Calculate the valency based on how many electrons the atom tends to lose, gain, or share to attain a full octet or stable configuration.
Example: Element with Atomic Number 26 (Iron, Fe)
- Electron Configuration of Fe (Z = 26):
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶
Or grouped: [Ar] 4s² 3d⁶ - Valence Shell:
The 4s and 3d electrons are considered in bonding for transition elements. Fe has 2 electrons in the 4s subshell and 6 in the 3d subshell. - Valency Determination:
Transition metals may show variable valency. Iron can lose two electrons (4s²) to form Fe²⁺ or three electrons (4s² and one 3d) to form Fe³⁺.
Therefore, Fe has valencies of 2 and 3.
Key Concepts:
- Valency refers to the combining capacity of an element.
- For main group elements, valency is usually equal to the number of electrons required to complete an octet (8 electrons) or duplet (2 electrons for hydrogen and helium).
- For transition elements (atomic number > 20), valency may vary due to the involvement of d-orbitals.
- Common valency for a transition metal is determined by common oxidation states.
Conclusion:
For elements with atomic number greater than 20, determining valency requires examining the full electron configuration, especially the d-orbitals for transition metals. These elements often show variable valency, depending on the chemical context and stability of oxidation states.
