Question

Why does hydrogen occur in a diatomic form rather than in a monoatomic form under normal conditions?

Short answer

Hydrogen is diatomic (H₂) to achieve a stable electron configuration.

Step-by-step solution

Identify the Electron Configuration of Hydrogen

Hydrogen has only one electron and its electron configuration is 1s¹. This means it has one electron in its outer shell, which makes it highly reactive because it seeks to stabilize that outer shell by filling it with two electrons.

Discuss the Concept of Chemical Stability

Atoms strive to achieve a stable electron configuration, typically through the octet rule which states that atoms tend to form bonds until they are surrounded by eight electrons. However, for hydrogen, it seeks only two electrons to fill its outer shell, achieving a stable configuration similar to helium.

Explain the Formation of Covalent Bonds

Since hydrogen has only one electron, it can pair with another hydrogen atom's electron to achieve a full outer shell. This pairing results in a covalent bond, where the two hydrogen atoms share their electrons, forming a molecule known as diatomic hydrogen (H₂).

Conclude with Molecular Form Over Monoatomic Form

In a diatomic form, hydrogen achieves stable electron configuration through the formation of covalent bonds, minimizing its energy state. Therefore, under normal conditions, hydrogen naturally occurs in diatomic form (H₂) because it is more energetically favorable than existing as monoatomic hydrogen.

Key concepts

Electron Configuration

Each element in the periodic table has a unique electron configuration, which is essentially the arrangement of electrons around its nucleus. For hydrogen, the simplest of all elements, this configuration is represented as 1s¹. This means hydrogen has a single electron in its first and only shell.

• The number before the letter (in this case, '1') indicates the energy level or shell.
• The letter 's' denotes the type of subshell that houses the electron.
• The superscript, '¹', indicates that there is one electron in that subshell.

This solitary electron in hydrogen’s outer shell makes it highly reactive. Since atoms generally strive for a full outer shell, hydrogen is eager to find another electron to share and stabilize its configuration. For hydrogen, reaching stability involves pairing this lone electron with another, forming a bond to complete its first shell.

Chemical Stability

Chemical stability is a concept that describes the tendency of an atom to resist changes in its electron configuration. Atoms aim to achieve a stable state, typically by having a fully filled outer shell or attaining a configuration similar to the noble gases. This stable state minimizes energy and increases the atom's resistance to reacting with others.
For most atoms, this involves reaching the 'octet' configuration (eight electrons in their outer shell). However, hydrogen is an exception:

• Hydrogen aims for a duet, meaning it seeks only two electrons to fill its outer shell — akin to helium, which is chemically inert.
• This quest for stability drives hydrogen to seek bonds, often forming molecules with other elements.

Achieving a stable electron arrangement reduces an atom’s potential energy and increases its chemical stability. For hydrogen, this is done by forming pairs through bonding.

Covalent Bonds

A covalent bond is a type of chemical bond where atoms share pairs of electrons. In the case of hydrogen, each atom possesses just one electron but needs another to become stable. When two hydrogen atoms come together, they each provide an electron, resulting in a shared pair — a covalent bond.
This covalent sharing occurs because:

• Both hydrogen atoms achieve a complete outer shell of two electrons.
• Through sharing, they reach a more stable energy state as a molecule rather than separate atoms.
• Two atoms of hydrogen bonded together form diatomic hydrogen, or H₂, which is more energetically favorable.

These shared electrons allow each hydrogen to "feel" as though it has filled its outer shell, greatly increasing its stability. That's why under normal conditions, hydrogen is found in this diatomic state, enhancing both its stability and energy efficiency.