The element having lowest `IE_(1)`

Options

A. (a) Fe
B. (b) Co
C. (c) Ni
D. (d) Cu

Answer

To determine which element has the lowest first ionization energy (IE₁) among iron, cobalt, nickel, and copper, we will follow these steps:

### Step 1: Understand Ionization Energy
Ionization energy is the energy required to remove the outermost electron from a neutral atom. The lower the ionization energy, the easier it is to remove an electron.

### Step 2: Identify the Elements and Their Atomic Numbers
The elements given are:
- Iron (Fe) - Atomic number 26
- Cobalt (Co) - Atomic number 27
- Nickel (Ni) - Atomic number 28
- Copper (Cu) - Atomic number 29

### Step 3: Write the Electronic Configurations
Next, we write the electronic configurations for each element:
- Iron: \( \text{Fe} = [\text{Ar}] 3d^6 4s^2 \)
- Cobalt: \( \text{Co} = [\text{Ar}] 3d^7 4s^2 \)
- Nickel: \( \text{Ni} = [\text{Ar}] 3d^8 4s^2 \)
- Copper: \( \text{Cu} = [\text{Ar}] 3d^{10} 4s^1 \)

### Step 4: Analyze the Trends in Ionization Energy
As we move from left to right across the transition metals, the ionization energy generally increases due to the increasing effective nuclear charge. However, there are exceptions due to electron pairing and exchange energy.

### Step 5: Consider Electron Pairing and Exchange Energy
- In iron, cobalt, and nickel, as we move from iron to nickel, the 3d electrons start to pair up, which can affect the ionization energy.
- Nickel has a unique case where the removal of an electron from the 4s orbital leads to a configuration that allows for exchange energy, which lowers its ionization energy compared to copper.

### Step 6: Determine the Lowest Ionization Energy
Based on the trends and the unique behavior of nickel:
- The order of ionization energies from highest to lowest is:
- Iron > Cobalt > Nickel > Copper
- However, due to the exchange energy effect, nickel has a lower ionization energy than copper.

### Conclusion
Thus, the element with the lowest first ionization energy (IE₁) among the given options is **Nickel (Ni)**.

### Final Answer
**Nickel (Ni)** has the lowest ionization energy among the given elements.

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