What will be the downward trend of ionization energy in group 13?

Answer

To analyze the downward trend of ionization energy in Group 13 elements, we will follow these steps:

### Step 1: Identify Group 13 Elements
Group 13 of the periodic table includes the elements: Boron (B), Aluminum (Al), Gallium (Ga), Indium (In), and Thallium (Tl).

### Step 2: Define Ionization Energy
Ionization energy is defined as the amount of energy required to remove an electron from an isolated gaseous atom in its outermost shell.

### Step 3: General Trend of Ionization Energy
In general, ionization energy tends to decrease as you move down a group in the periodic table. This is primarily due to:
- An increase in atomic size (more electron shells).
- A decrease in effective nuclear charge experienced by the outermost electrons due to increased shielding from inner shell electrons.

### Step 4: Analyze the Trend in Group 13
1. **From Boron to Aluminum**:
- As we move from Boron to Aluminum, the ionization energy decreases as expected due to the increase in atomic size and the shielding effect.

2. **Gallium**:
- Interestingly, Gallium has a slightly higher ionization energy than Aluminum. This is because Gallium has d orbitals that are not very effective at shielding the outer electrons from the nucleus. The presence of these d electrons leads to a stronger attraction between the nucleus and the outer electrons, resulting in higher ionization energy compared to Aluminum.

3. **From Gallium to Indium**:
- Moving from Gallium to Indium, the ionization energy decreases again. This is due to the increased shielding effect caused by additional 4d electrons, which outweighs the increased nuclear charge.

4. **From Indium to Thallium**:
- Finally, when moving from Indium to Thallium, the ionization energy increases again. This is because Thallium has additional 4f and 5d electrons, which do not shield the outer electrons effectively, leading to a stronger attraction between the nucleus and the outermost electrons.

### Step 5: Summarize the Trend
The order of ionization energy in Group 13 can be summarized as follows:
- Boron (B) > Aluminum (Al) > Gallium (Ga) > Indium (In) < Thallium (Tl)

### Conclusion
The downward trend of ionization energy in Group 13 is not straightforward due to the effects of electron shielding and the presence of d and f orbitals. The overall trend shows a decrease in ionization energy from Boron to Indium, with Gallium and Thallium exhibiting higher ionization energies than expected due to their unique electron configurations.

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