Question

Identify the element having highest ionization enthalpy.

• A. Ti
• B. Sc
• C. Zn
• D. Ni

Hint:

Ionization enthalpy generally increases across a period due to increasing effective nuclear charge. Elements with fully-filled ($s^2$, $p^6$, $d^{10}$) or half-filled ($p^3$, $d^5$) electron subshells exhibit extra stability, making it harder to remove an electron and thus resulting in higher ionization enthalpy compared to their neighbors.

Answer 1

The Correct Option is A

Step 1: Define ionization enthalpy. Ionization enthalpy (or ionization energy) is the minimum amount of energy required to remove the outermost electron from an isolated gaseous atom in its ground state. Generally, ionization enthalpy increases across a period due to increasing effective nuclear charge and decreasing atomic radius, and decreases down a group due to increasing atomic size and shielding effect.
Step 2: List electron configurations and atomic numbers of the given elements. The given elements are Ti (Titanium), Sc (Scandium), Zn (Zinc), and Ni (Nickel). All are transition metals in the 3d series. Atomic numbers and electronic configurations: \[ \text{Sc }(Z=21): [Ar]3d^1 4s^2 \] \[ \text{Ti }(Z=22): [Ar]3d^2 4s^2 \] \[ \text{Ni }(Z=28): [Ar]3d^8 4s^2 \] \[ \text{Zn }(Z=30): [Ar]3d^{10}4s^2 \]
Step 3: Analyze the trend across the 3d series. Ionization enthalpy generally increases across a period because effective nuclear charge increases and atomic size decreases. Although minor irregularities occur in transition metals due to electron repulsion and subshell stability, the general increasing trend still holds. Among the given elements, the order in the periodic table is: \[ \text{Sc<Ti<Ni<Zn} \]
Step 4: Focus on Zinc (Zn). Zinc has the configuration: \[ [Ar]3d^{10}4s^2 \] This represents a completely filled $3d$ subshell and filled $4s$ subshell, giving extra stability. Removing an electron from such a stable configuration requires comparatively higher energy. Therefore, Zinc has the highest first ionization enthalpy among Sc, Ti, Ni, and Zn.