Covalent bond

Nature of chemical interaction

The presence of stable chemical bonds between atoms forming molecules and complex crystals is an obvious and fundamental fact of matter structure. Absolutely all chemical bonds have an electromagnetic nature. It is precisely the electromagnetic interaction that holds particles together, ensuring the stability of both the simplest diatomic gases and complex polyatomic structures. Without these electromagnetic forces, the existence of the forms of matter familiar to us would be impossible.

Dative bonding mechanism

Usually, a chemical bond is formed when atoms provide each other with one unpaired electron each. However, there is a special pathway for the formation of a covalent chemical bond — the dative (coordinate covalent) mechanism. In this case, the shared electron pair is formed not through mutual exchange, but in a different way: one atom provides a completely ready electron pair, and the other atom provides its vacant orbital for it.

This mechanism plays a key role in chemistry. In particular, it is the formation of dative bonds that determines the acidic and basic properties of various substances, which is clearly seen in the example of the structure of the ammonium ion.

The dative mechanism is of immense importance in the structure of complex compounds. In such molecules, a chemical bond is formed between the central atom and the surrounding ligands. A classic example is potassium ferricyanide (red prussiate), whose formula is written as $\text{K}_3[\text{Fe}(\text{CN})_6]$.

In this molecule, the roles are distributed as follows:

• Central atom: Iron ($\text{Fe}$). It acts as an acceptor, providing as many as 6 vacant valence orbitals.
• Ligands: $\text{CN}$ groups (cyano groups). The carbon atoms in these groups act as donors — they transfer their lone electron pairs to the vacant orbitals of the iron atom, forming a strong complex.

Multiple chemical bonds

Depending on their electronic structure and the need to complete valence shells, atoms in molecules can be connected not only by single bonds, but also by multiple bonds. These include double and triple bonds.

An example of a molecule with double bonds is carbon dioxide: $\text{O}=\text{C}=\text{O}$. Here, the carbon atom is connected to each oxygen atom by a double bond. A triple bond is characteristic, for example, of the acetylene molecule, where two carbon atoms are tightly bonded together: $\text{H}-\text{C}\equiv\text{C}-\text{H}$.

Relationship between bond energy and chemical activity

The strength of a chemical bond directly determines how actively a substance will enter into chemical reactions. The higher the bond energy, the more stable the molecule. A comparative characterization of simple gases based on the strength of their molecules perfectly illustrates this pattern:

1. Nitrogen ($N_2$): This molecule has the highest bond energy among the gases considered. Due to its extreme strength, nitrogen is chemically inert and under normal conditions enters into only a very small number of chemical reactions.
2. Oxygen ($O_2$): The bond in this molecule is less strong. Due to this, oxygen exhibits moderate chemical activity and is capable of participating in numerous processes.
3. Fluorine ($F_2$): Possesses the least strong molecule with very low bond energy. This makes fluorine an extremely active element. If fluorine enters the atmosphere, it instantly reacts with any surrounding gases and very quickly disappears in its free form.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Detailed mechanism of formation of classical covalent chemical bonds
• Acid-base properties and electronic structure of the ammonium ion
• Structural features and classification of complex compounds
• The effect of double and triple bonds on the spatial structure of molecules

Other topics in "Chapter 5. Structure of Matter"

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