Chemical Bonding Principles and Atomic Structures

Chemical Bonding and Atomic Configurations

How the elements reach a noble gas configuration gives rise to three types of chemical bonds between atoms: ionic, covalent, and metallic.

• Chemical bonds: All the forces that hold together atoms when they form molecules or crystals, as well as the forces that hold together the molecules when present in a liquid or solid.
• Octet rule (Gilbert N. Lewis): Atoms are bonded with each other to achieve eight electrons in their valence level.

The Nature of Ionic Bonding

Ionic bonds form when atoms combine to reach the noble gas configuration. Atoms lose electrons to reach the noble gas configuration or gain electrons to reach it. One electronegative atom will tend to gain electrons and form a negative ion (anion). One very electropositive atom will tend to lose electrons and form a positive ion (cation).

• Crystal lattice: It is a very stable structure in which positive ions are surrounded by the greatest possible number of negative ions and vice versa.
• The formula of an ionic compound indicates the proportion in which atoms are combined; it is an empirical formula because these compounds do not form molecules.
• Coordination index: The number of ions of one sign that surround an ion of the opposite sign.

Characteristics of Ionic Compounds

• Solid state: They are solid at room temperature; their high melting point is related to the stability of the crystal lattice.
• Hardness and fragility: They are hard and fragile. Hardness is the resistance to scratching, while fragility is related to the resistance to blows.
• Conductivity: They do not conduct electricity in a solid state, but they do when they are fused or in solution. For a material to be conducting, it should allow for the movement of electric charges.
• Solubility: Most ionic compounds are soluble in water and are insoluble in non-polar solvents (such as benzene or gasoline).

Covalent Bonds and Energy Stability

A covalent bond is formed when atoms combine, each tending to achieve a noble gas configuration. In that case, the only way to bind two atoms is for electrons to be shared at their level of valence.

To move a particle to a higher energy area, it should receive external power. Any system always tends to lose energy to achieve the minimum values which achieve stability.

Quantum Principles of Atomic Structure

• Pauli Exclusion Principle: In an atom, no two electrons can have the same four quantum numbers.
• Hund's Rule: When the principle of minimum energy and the Pauli exclusion principle are applied, different configurations can be given; the most favorable is the one that allows the greatest number of electrons with the same spin (unpaired).