Fundamental Principles of Chemical Bonding

Metallic Bonds and Their Characteristics

The basic characteristics of metallic components are produced by the nature of metallic bonding. These include:

• They are usually solid at room temperature, except mercury, and their melting and boiling points vary greatly.
• The thermal and electrical conductivities are very high (this is explained by the enormous mobility of their valence electrons).
• They have a metallic shine, as they are less electronegative.
• They are ductile and malleable (the great mobility of the valence electrons allows the metal cations to move without producing a break).
• They can emit electrons when they receive energy as heat.
• They tend to lose electrons when they receive light quanta (photons) in their outer layers, a phenomenon known as the photoelectric effect.

The metallic bond is characteristic of metallic elements; it is a strong, primary bond formed between elements of the same species. Atoms, being so close to each other, interact with their nuclei and electron clouds packaged in three dimensions, so they are surrounded by such clouds. These free electrons are responsible for metals having high electrical and thermal conductivity, since they can move easily if they come in contact with an electrical source. They present brightness and are malleable.

Covalent Bonds and Molecular Structures

The union between valence atoms produces a threefold bond through anions and cations. The model assumes that in a covalent bond, the atoms share electrons to complete the valence layer. The link is represented by Lewis diagrams.

Covalent bonds occur in:

Molecular Substances

• They are liquids or gases at ambient temperature; the bond between atoms is very strong.
• They are water-insoluble because they have no ions.
• They do not conduct electricity because they have no electric charge.

Covalent Crystals

Examples include diamond and graphite.

• They are solid at ambient temperature with high melting and boiling points due to strong links.
• They are water-insoluble.
• They do not conduct electricity.

Chemical Links: Ionic Bonds

An ionic bond occurs between atoms of elements with very different electronegativities. The metal atoms lose electrons easily when in contact with highly electronegative atoms, forming the salt bridge: very electronegative elements with less electronegative ones.

Properties of Ionic Bonds

• They are solid at room temperature.
• They have high melting and boiling points.
• They are hard and brittle.
• They are water-soluble, and their solutions are conductors (though the solids are not).