Atomic hydrogen combaines with almost all elements but molecular hydrogen does not. Explain.

Explanation

### Step-by-Step Solution:

1. **Understanding Atomic Hydrogen**:
- Atomic hydrogen refers to individual hydrogen atoms (H) that exist in their atomic form. Each hydrogen atom has one electron and needs one more electron to achieve a stable electronic configuration, similar to that of helium.

2. **Reactivity of Atomic Hydrogen**:
- Due to its need for an additional electron, atomic hydrogen is highly reactive. It can combine with almost all elements through various mechanisms:
- **Loss of an Electron**: Atomic hydrogen can lose its single electron to form a positively charged ion (H⁺).
- **Gain of an Electron**: It can also gain an electron to form a negatively charged ion (H⁻).
- **Covalent Bond Formation**: Atomic hydrogen can share its electron with other atoms, forming covalent bonds.

3. **Understanding Molecular Hydrogen**:
- Molecular hydrogen (H₂) consists of two hydrogen atoms bonded together. The bond between these two atoms is a covalent bond, and it is characterized by a high bond dissociation energy of approximately 435.88 kJ/mol.

4. **Stability of Molecular Hydrogen**:
- The high bond dissociation energy indicates that the H-H bond is strong and stable. As a result, molecular hydrogen is less reactive compared to atomic hydrogen. At room temperature, molecular hydrogen does not readily react with most elements, making it behave almost inert.

5. **Conclusion**:
- In summary, atomic hydrogen is highly reactive due to its unstable electronic configuration and its ability to form various types of bonds. In contrast, molecular hydrogen is stable and does not react easily with other elements due to the strong H-H bond.