On this page:
Introduction What is an Electron Sharing Reaction? Covalent Bonding Structure of Molecules Bond Polarity and Molecular Polarity Factors Affecting Electron Sharing Bond Strength and Bond Energy Multiple Bonds Reactions with Resonance Coordinate (Dative) Covalent Bonds Intermolecular Forces Why Electron Sharing Reactions Are Important Summary
Have you ever wondered why oxygen exists as O₂ in the air, or why water sticks together? The answer to those questions is in the way the atoms share electrons. The sharing of electrons is the most common way to create a chemical bond, and these reactions explain the stability of just about every molecule in the world around us.
An electron sharing reaction is a chemical reaction in which two or more atoms share electrons, in order to achieve a stable electron configuration. In contrast to ionic reactions, in which identical or different atomic species lose or gain electrons, in an electron sharing reaction a covalent bond is formed, and the atoms in the bond 'capture' and hold the electrons being shared.
When two hydrogen atoms come together, they each share one of their electrons, and they both get to fill up their outer shells, bonding together to create H₂.
The most frequent result of chemical reactions involving electron sharing are covalent bonds.
One pair of electrons shared between two bonded atoms
Example: H–H (hydrogen)
Two pairs of electrons shared between two atoms
Example: O=O (oxygen)
Three pairs of electrons shared between two atoms
Example: N≡N (nitrogen)
Covalent Bonds Basics:
The form and the structure of the molecules are the result of the reactions of shared electrons. The predicted shape is based on VSEPR Theory (Valence Shell Electron Pair Repulsion):
Electron pairs push each other and are neutral to the surrounding molecules. This repulsion drives the molecule to orient in a way that electron pairs are as separate as possible.
Common Shapes:
Sharing of electrons is not always an equal activity. At times, one of the atoms will capture the shared electrons with more force than the other.
Electronegativity is the strength of an atom to pull the shared electrons towards itself.
The shape of a molecule and polarity of the bonds will determine the polarity of the molecule.
Several factors influence the stability of a bond:
A more stable, low energy state will result when atoms share electrons. Therefore, electron sharing reactions will always release energy.
Bond energy is defined as the amount of energy needed to break one mole of a given bond in a given molecule.
A bond is considered stronger the more energy is required to break it. Therefore, triple bonds have a higher bond energy than single bonds.
The energy changes that occur in chemical reactions when electrons are shared accounts for the reason some chemical reactions are said to be exothermic (give off energy) or endothermic (take in energy).
In some instances, in order to satisfy the octet rule, the involved atoms share several pairs of electrons:
A rule of thumb: multiple bonds are stronger and shorter than single bonds. Additionally, molecules that contain multiple bonds have restricted rotation compared to single bonded molecules, impacting geometry and reactivity.
Some molecules cannot be represented by a single Lewis structure as they are said to have multiple resonance structures. For such molecules, the arrangement of electrons can vary.
Example: O₃ (ozone)
In some chemical reactions involving electron sharing, both electrons in the shared pair come from one of the atoms:
In such a reaction, the nitrogen atom donates a lone pair to form a coordinate bond with the proton. Covalent bonds have a regular bond formation process.
The sharing of electrons also impacts intermolecular forces:
Covalent bond formation (electron sharing) explains:
Everyday Examples:
Important Points to Note
The reaction of molecular bonds and the sharing of electrons is not an abstract idea; it shows the world around us at a molecular scale.