The elements in increasing order of ionization energy are

Options

A. Cu, Ag, Au
B. Ag, Cu, Au
C. Au, Cu, Ag
D. Ag, Au, Cu

Answer

To determine the increasing order of ionization energy for the elements copper (Cu), silver (Ag), and gold (Au), we can follow these steps:

### Step 1: Understand Ionization Energy
Ionization energy is defined as the amount of energy required to remove an electron from an atom in its gaseous state. Generally, higher nuclear attraction leads to higher ionization energy.

**Hint:** Remember that ionization energy increases with greater nuclear charge and decreases with increased atomic size.

### Step 2: Examine the Electronic Configurations
- **Copper (Cu):** Argon (Ar) 3d^10 4s^1
- **Silver (Ag):** Krypton (Kr) 4d^10 5s^1
- **Gold (Au):** Xenon (Xe) 4f^14 5d^10 6s^1

**Hint:** Look at the outermost electrons in each element's electronic configuration to assess how tightly they are held by the nucleus.

### Step 3: Analyze Shielding Effect
The shielding effect refers to the reduction in effective nuclear charge experienced by outer electrons due to the presence of inner electrons. The order of shielding effect generally decreases from S to P to D to F orbitals.

- **Cu and Ag:** Both have D electrons, which provide some shielding.
- **Au:** Has F electrons, which provide more shielding than D electrons.

**Hint:** Recall that less shielding means outer electrons feel a stronger nuclear charge, which can increase ionization energy.

### Step 4: Compare Ionization Energies
1. **Gold (Au):** Despite having a larger atomic size, the presence of F electrons leads to a significant nuclear charge experienced by the outermost electron, resulting in a higher ionization energy.
2. **Copper (Cu):** Has a higher ionization energy than silver due to its smaller size and less shielding effect compared to silver.
3. **Silver (Ag):** Has the lowest ionization energy among the three due to increased atomic size and more shielding.

**Hint:** Consider that as you move down the group in the periodic table, ionization energy generally decreases.

### Step 5: Establish the Order
Based on the analysis:
- Gold (Au) has the highest ionization energy.
- Copper (Cu) has a higher ionization energy than silver (Ag).
- Silver (Ag) has the lowest ionization energy.

Thus, the increasing order of ionization energy is:
**Ag < Cu < Au**

**Final Answer:** The elements in increasing order of ionization energy are Silver (Ag), Copper (Cu), and Gold (Au).