Bonding and antibonding orbitals are important parts of a theory called molecular orbital (MO) theory. This theory helps us understand how molecules are made and why they are stable.

Bonding Orbitals

• What They Are: Bonding orbitals happen when atomic orbitals come together in a way that adds to their strength. This creates more electron density, or more "buzz" of electrons, between two atoms.
• Energy Levels: Bonding orbitals have lower energy than the original atomic orbitals. This lower energy is important for making molecules stable.
• Example: Take the hydrogen molecule ($H_2$). The bonding orbital here is called $\sigma_{1s}$. It forms from two $1s$ atomic orbitals overlapping. The bond energy for $H_2$ is about 436 kJ/mol, which shows how strong the bond is.

Antibonding Orbitals

• What They Are: Antibonding orbitals form when atomic orbitals come together in a way that cancels each other out. This creates a place where there’s less electron density between the atoms.
• Energy Levels: Antibonding orbitals have higher energy than the atomic orbitals they come from. This makes the molecule less stable.
• Notation: The antibonding orbital linked to the $1s$ orbital is shown as $\sigma^*_{1s}$.
• Energy Difference: The energy difference between bonding and antibonding orbitals can be calculated using the formula: $\Delta E = E_{bonding} - E_{antibonding}$

Impact on Molecular Stability

• Bond Order: We can figure out the bond order using this formula: $\text{Bond Order} = \frac{(N_b - N_a)}{2}$ Here, $N_b$ is the number of electrons in bonding orbitals, and $N_a$ is the number in antibonding orbitals.
• For example, in oxygen ($O_2$), there are 10 electrons in bonding orbitals and 6 in antibonding orbitals. This gives a bond order of: $\text{Bond Order} = \frac{(10 - 6)}{2} = 2$

Knowing about bonding and antibonding orbitals is really important. They help explain how stable molecules are, how they react with other substances, and what physical properties they have.