The second ionization enthalpy of which of the following alkaline earth metals is the highest?

Options

A. Ba
B. Mg
C. Ca
D. Be

Answer

To determine which alkaline earth metal has the highest second ionization enthalpy, we can follow these steps:

### Step 1: Understand the Configuration of Alkaline Earth Metals
Alkaline earth metals have the general electronic configuration of \( ns^2 \), where \( n \) is the principal quantum number. This means they have two electrons in their outermost s orbital.

### Step 2: Define Ionization Enthalpy
Ionization enthalpy is the energy required to remove an electron from an atom. The first ionization enthalpy involves removing one electron, while the second ionization enthalpy involves removing a second electron from the already positively charged ion.

### Step 3: Analyze the Second Ionization Process
For alkaline earth metals, after the first ionization, the atom becomes a \( M^+ \) ion (where \( M \) is the metal). The second ionization involves removing an electron from a configuration that is closer to a noble gas configuration, which is more stable.

### Step 4: Consider the Size of the Atoms
The size of the alkaline earth metals increases down the group from beryllium to barium. Smaller atoms have a stronger attraction between the nucleus and the electrons due to shorter distance, making it harder to remove an electron.

### Step 5: Identify the Element with the Highest Second Ionization Enthalpy
- **Beryllium (Be)** is the smallest alkaline earth metal, and thus has the highest attraction between its nucleus and electrons. This means that removing the second electron from beryllium will require the most energy, resulting in the highest second ionization enthalpy.
- As we move down the group to magnesium, calcium, strontium, and barium, the atomic size increases, and the second ionization enthalpy decreases.

### Conclusion
The alkaline earth metal with the highest second ionization enthalpy is **Beryllium (Be)**.

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