Molecular, Ionic Covalent and Metallic Solids

In this section on intermolecular forces, the structures of molecular solids, which are solids made up of individual molecules, are discussed. Hydrogen bonds, dispersion forces, and other dipolar forces hold these molecules together depending upon the type of constituent molecules. The molecules stack together in a configuration that minimizes their total energy. Ice, which relies heavily on hydrogen bonding, and polyethene, which relies heavily on dispersion forces, are two examples of such solids. Because the connections between molecules are easily broken, molecular solids are often soft and have low melting temperatures unless hydrogen bonds are present. Dispersion forces are present between nonpolar molecules and dipole interactions exist between polar molecules

Properties

Ionic and covalent connections are stronger than dipole forces. Molecular solids have low melting temperatures, often less than 300 degrees Celsius, due to relatively weak intermolecular interactions. Organic solvents tend to dissolve molecular solids. The majority of molecular solids are low-density electrical insulators.

Ionic Solids

These solids are made up of oppositely charged ions stacked in alternate spaces with unequal atomic sizes and strong electrostatic tension, making them electrically inert in solid form. The aggregation of anions and cations in a geometrical pattern imparts a crystalline appearance at room temperature. They are very closely packed and have strong interaction between them.

They never exist in a liquid or gaseous state at normal temperatures and pressures because their ions are immobile due to a strong electrostatic interaction between oppositely charged ions. Because electron mobility is limited, these compounds can never exist in a gaseous or liquid state.

Ionic Solids Characteristics

• When ionic solids are in their solid state, they do not conduct electricity. This is due to the strong electrostatic tension between alternatively organized cations and anions, making electron mobility difficult and preventing conduction. The ions are securely bound in their fixed locations in a crystal lattice.

• However, when ionic solids are in solution or fused, they conduct electricity—the kinetic energy of ions increases as the temperature rises. When the compound enters the solution or molten state, the ionic kinetic energy is so high that it overcomes the attractive forces and the well-organized crystalline structure, allowing the ions to become free and move around under the influence of an applied electric field. Their charged nature helps them conduct charge in this case.

• Ionic solids are relatively hard and have low volatility and high melting and boiling temperatures. This is due to the strong electrostatic force between the cations and anions, which keeps them in their fixed locations. This makes it extremely difficult for them to move around.

• The electrostatic force between the anions and cations determines solubility in polar and non-polar liquids. The high dielectric constant of the polar solvent reduces the force in the case of ionic solids. The ions can travel freely and produce solvated ions because of the lower electrostatic force of attraction caused by the high dielectric constant values of the solvent. Because of their low dielectric constants, ionic solids are insoluble in non-polar liquids.

• Because water possesses a dipole, the positive end of the dipole interacts with the negative ion of the ionic solids. In contrast, the negative end of the dipole interacts with the positive ion of the same ionic crystals, allowing ionic solids to dissolve in polar compounds like water.

Covalent Solids

Solids bound together through covalent bonds are covalent solids or network solids. As a result, their electrons are confined, and their atoms are arranged in set geometries. The breakage of covalent sigma bonds can cause distortion away from this geometry. As a result, covalent solids have a very high melting point. They’re usually exceedingly hard materials that will shatter rather than alter shape smoothly. Hence, they are rigid and brittle. And diamond and silica are examples of covalent solids.

Covalent Molecular solids Properties

• Melting and boiling points are both high.
• Solid forms that are hard and brittle.
• Thermal and electrical conductivity are both poor.(except graphite)

Diamond and graphite, as well as fullerenes and other solids, are examples of this class.

The hardest natural substance on the planet is diamond. It is an electrical non-conductor. Being used as an abrasion for sharpening hard equipment and the production of dyes and tungsten filaments for light bulbs.

Metallic Solids

Metal atoms create metallic solids like copper, aluminium, and iron crystals. The homogeneous distribution of atomic nuclei within a “sea” of delocalised electrons is often used to explain the structure of metallic crystals. The atoms in a metallic solid are kept together with a special force known as metallic bonding, which results in a wide range of beneficial bulk properties.

High electrical and thermal conductivity, metallic sheen, and malleability characterize all metallic substances. Many are extremely tough and powerful. They do not shatter due to their malleability and make useful construction materials. Metals have a wide range of melting points. Mercury is a liquid at ambient temperature, and alkali metals melt below 200 degrees Celsius. Several post-transition metals have low melting points, whereas transition metals melt at temperatures beyond 1000 degrees Celsius. These variations reflect variances in metallic bonding strengths between metals.

Metallic Solids have the following characteristics:

• Their melting and boiling points are both very high.
• They have a lot of thermal conductivity.
• They have a high conductivity of electricity.
• They are ductile and malleable.

Conclusion

Solids are classified as ionic, molecular, covalent, or metallic. The bonding intensity is represented in the lattice energy of ionic solids, which are made up of positive and negative ions bonded together by electrostatic forces. Dipole-dipole interactions, hydrogen bonds, & London dispersion forces are all relatively weak forces that hold molecular solids together.

Covalent solids comprise 2- or three-dimensional networks of atoms bound together by covalent connections and have high melting temperatures.