Question

Find the EAN of Zn in $[Zn(NH_3)_4]^{2+}$?

• A. 38
• B. 37
• C. 36
• D. 35

Hint:

The EAN rule suggests that complexes are highly stable if their EAN perfectly matches the atomic number of the next noble gas. In this case, 36 is the exact atomic number of the noble gas Krypton (Kr).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks us to calculate the Effective Atomic Number (EAN) of the central zinc ion in the specified tetramminezinc(II) coordination complex.

Step 2: Key Formula or Approach:
The formula for calculating EAN is:
$$EAN = Z - X + Y$$
Where:
$Z$ = Atomic number of the central metal atom.
$X$ = Oxidation state (number of electrons lost by the metal).
$Y$ = Total number of electrons donated by all the ligands ($2 \times$ coordination number).

Step 3: Detailed Explanation:
1. Determine Z: The atomic number of Zinc (Zn) is 30.
2. Determine X: Ammonia ($NH_3$) is a neutral ligand. The overall charge of the complex is +2. Therefore, the oxidation state of Zn is +2. So, $X = 2$.
3. Determine Y: There are 4 ammonia ligands. Each ammonia molecule donates a pair of electrons (2 electrons) to form a coordinate bond.
$Y = 4 \text{ ligands} \times 2 \text{ electrons/ligand} = 8$ electrons.
4. Calculate EAN:
$$EAN = 30 - 2 + 8$$
$$EAN = 28 + 8 = 36$$

Step 4: Final Answer:
The Effective Atomic Number is 36, which matches option (c).