How Covalent Bonds Form Using the Octet Rule

Covalent bonds form when two nonmetal atoms share electrons to achieve a stable electron configuration, often following the octet rule. The octet rule states that atoms tend to form bonds until they have eight valence electrons, resembling the electron configuration of noble gases.

Step 1: Understanding Electron Sharing - Atoms with similar tendencies to attract electrons (like nonmetals) will share electrons rather than transfer them.<br /> - In a covalent bond, each atom contributes one or more electrons to achieve a full valence shell.

Step 2: Formation of a Covalent Bond - When two atoms approach each other, their outermost (valence) orbitals begin to overlap.<br /> - The shared electrons are attracted to both nuclei, which stabilizes the molecule.<br /> - The optimal bond length is the point where attractive forces (between electrons and nuclei) are balanced with repulsive forces (between like charges).

Example: Hydrogen (H₂) Molecule - Each hydrogen atom has one valence electron. - By sharing their single electrons, both achieve a stable configuration with two electrons, like helium.

H • + • H → H:H (or H—H)

This stable bond occurs at 74 pm, the optimal distance where attractive and repulsive forces are balanced.

Step 3: Applying the Octet Rule - Hydrogen (H): Only needs 2 electrons (duet rule).<br /> - Other nonmetals (C, N, O, etc.):Typically follow the octet rule by sharing enough electrons to reach 8 valence electrons.

Example: Fluorine (F₂) Molecule - Each fluorine atom has 7 valence electrons. - By sharing one unpaired electron, each atom completes its octet.

F • + • F → F:F (or F—F)

Each fluorine now has one bonding pair(shared electrons) and three lone pairs(non-bonding electrons).

Key Points - Single bonds involve one shared pair of electrons (e.g., H₂, F₂).<br /> - Atoms can also form **double or triple bonds if they need to share more pairs of electrons to satisfy the octet rule (e.g., O₂, N₂).<br /> - Some elements like Boron (B)or Beryllium (Be)may form stable molecules without a full octet, while elements in Period 3 or higher can form expanded octets

By sharing electrons, nonmetal atoms create stable molecules that satisfy the octet rule, ensuring each atom reaches a stable electron configuration.

Lewis Structures Chemists frequently use Lewis structures to represent covalent bonding in molecular substances. For example, the Lewis symbols of two separate hydrogen atoms are as follows:

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The Lewis structures of two hydrogen atoms sharing electrons looks like this:

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We can use circles to show that each H atom has two electrons around the nucleus, completely filling each atom’s valence shell:

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Because each H atom has a filled valence shell, this bond is stable, and we have made a diatomic hydrogen molecule. For simplicity’s sake, it is common to represent the covalent bond with a dash, instead of with two dots: