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Hydrogen, the simplest and most abundant element in the universe, is fundamental to numerous chemical processes. Each hydrogen atom consists of a single proton and a single electron. Because its atomic number is 1, hydrogen has only one electron located in its outermost shell. In its natural state, this electron configuration makes hydrogen unstable because it seeks to fill or share its electron to achieve a more stable electron configuration.

According to quantum mechanics, the most stable configuration for any atom's outer shell is to have two electrons, which would fill the first shell (the K shell) and mimic the stable configuration of helium. However, hydrogen naturally occurs with just one electron, making it reactive as it seeks to achieve stability by gaining one more electron.

Covalent bonding is a critical concept in creating stable molecules from single atoms, such as hydrogen. In covalent bonds, atoms share pairs of electrons to fill their outer electron shells and achieve stability. This type of bonding is common among nonmetal atoms, which like to attain stable electron configurations similar to those of noble gases.

When two hydrogen atoms meet, each atom contributes its single electron to form a shared pair of electrons. This sharing of electrons forms a covalent bond. As a result, each hydrogen atom effectively attains two electrons in its outermost shell, achieving the electron configuration of helium, which is a noble gas. This shared electron pair is situated between the two hydrogen nuclei and acts as a strong cohesive force, resulting in the formation of a diatomic molecule, (H_2).

Electron configuration refers to the distribution of electrons in an atom's orbitals. For hydrogen, with its single electron, the electron configuration is quite simple: 1s¹. This indicates its one electron occupies the first (and only) orbital available, making hydrogen atoms eager to either share or gain an electron to fill this shell.

In the context of a diatomic hydrogen molecule (H_2), both hydrogen atoms share their single electrons, thereby achieving a full shell of two electrons. This mirrors the electron configuration of helium, which is represented as 1s².

• Basic configuration of hydrogen in isolation: 1 electron in the 1s orbital.
• In (H_2), each hydrogen complements the other's electron to jointly occupy the 1s orbital with two electrons.

This shared approach results in a much more stable configuration, keeping the hydrogen atoms bonded together.