The actinides which has half filled 5f-orbitals are

Options

A. only Am
B. only Cm
C. both Am and No
D. Both Am and Cm

Answer

To determine which actinides have half-filled 5f orbitals, we need to analyze the electronic configurations of the actinides. The actinides are elements with atomic numbers ranging from 90 (thorium) to 103 (lawrencium), and their general electronic configuration can be expressed as:

\[ \text{[Rn]} \, 5f^{1-14} \, 6d^{0-1} \, 7s^2 \]

Here, the 5f subshell can hold a maximum of 14 electrons, and a half-filled subshell would contain 7 electrons.

### Step-by-Step Solution:

1. **Identify the Actinide Series**: The actinides consist of elements from atomic number 90 (thorium) to 103 (lawrencium). The elements are:
- Thorium (Th, 90)
- Protactinium (Pa, 91)
- Uranium (U, 92)
- Neptunium (Np, 93)
- Plutonium (Pu, 94)
- Americium (Am, 95)
- Curium (Cm, 96)
- Berkelium (Bk, 97)
- Californium (Cf, 98)
- Einsteinium (Es, 99)
- Fermium (Fm, 100)
- Mendelevium (Md, 101)
- Nobelium (No, 102)
- Lawrencium (Lr, 103)

2. **Determine the Electron Configuration**: The electron configurations for the actinides can be summarized as follows:
- Th: [Rn] 6d² 7s²
- Pa: [Rn] 5f² 6d¹ 7s²
- U: [Rn] 5f³ 6d¹ 7s²
- Np: [Rn] 5f⁴ 6d¹ 7s²
- Pu: [Rn] 5f⁵ 6d¹ 7s²
- Am: [Rn] 5f⁶ 7s²
- Cm: [Rn] 5f⁷ 7s²
- Bk: [Rn] 5f⁷ 6d¹ 7s²
- Cf: [Rn] 5f⁹ 7s²
- Es: [Rn] 5f¹⁰ 7s²
- Fm: [Rn] 5f¹¹ 7s²
- Md: [Rn] 5f¹² 7s²
- No: [Rn] 5f¹³ 7s²
- Lr: [Rn] 5f¹⁴ 7s²

3. **Identify Half-Filled 5f Orbitals**: A half-filled 5f subshell would mean that there are 7 electrons in the 5f orbital. Looking at the configurations, we find:
- Np (Neptunium) has 4 electrons in the 5f subshell.
- Pu (Plutonium) has 5 electrons in the 5f subshell.
- Am (Americium) has 6 electrons in the 5f subshell.
- Cm (Curium) has 7 electrons in the 5f subshell.

4. **Conclusion**: The only actinide with a half-filled 5f orbital is Curium (Cm), which has the configuration of [Rn] 5f⁷ 7s².

### Final Answer:
The actinide that has half-filled 5f orbitals is **Curium (Cm)**.