Bond order of helium molecule is

Options

A. 0
B. 1
C. `1/2`
D. 1

Answer

To determine the bond order of the helium molecule (He2), we will follow these steps:

### Step 1: Understand the concept of bond order
Bond order is calculated using the formula:
\[ \text{Bond Order} = \frac{(N_b - N_a)}{2} \]
where \(N_b\) is the number of electrons in bonding orbitals and \(N_a\) is the number of electrons in anti-bonding orbitals.

### Step 2: Identify the atomic number of helium
Helium has an atomic number of 2, which means each helium atom has 2 electrons. Therefore, for a helium molecule (He2), the total number of electrons is:
\[ 2 \text{ (from first He)} + 2 \text{ (from second He)} = 4 \text{ electrons} \]

### Step 3: Construct the Molecular Orbital (MO) diagram for He2
The molecular orbital diagram for He2 consists of:
- One bonding molecular orbital: \( \sigma_{1s} \)
- One anti-bonding molecular orbital: \( \sigma^*_{1s} \)

### Step 4: Fill the molecular orbitals with electrons
According to the Aufbau principle, electrons fill the lowest energy orbitals first:
- The \( \sigma_{1s} \) bonding orbital will be filled first with 2 electrons.
- The \( \sigma^*_{1s} \) anti-bonding orbital will then be filled with the remaining 2 electrons.

So, we have:
- \( N_b = 2 \) (electrons in the bonding orbital)
- \( N_a = 2 \) (electrons in the anti-bonding orbital)

### Step 5: Calculate the bond order
Using the bond order formula:
\[ \text{Bond Order} = \frac{(N_b - N_a)}{2} = \frac{(2 - 2)}{2} = \frac{0}{2} = 0 \]

### Conclusion
The bond order of the helium molecule (He2) is **0**. This indicates that there is no stable bond formed between the two helium atoms.

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