Question

What kinds of attractive forces exist between particles in (a) molecular crystals, (b) ionic crystals, and (c) covalent crystals?

Short answer

Molecular crystals have London dispersion forces, dipole-dipole interactions, and hydrogen bonds; ionic crystals have ionic bonds; covalent crystals have covalent bonds.

Step-by-step solution

Identifying Forces in Molecular Crystals

In molecular crystals, the particles are molecules held together by intermolecular London dispersion forces, dipole-dipole interactions, and hydrogen bonds if apt molecules are present.

Determining Forces in Ionic Crystals

Ionic crystals are composed of positively and negatively charged ions. The attractive forces between these ions are electrostatic in nature and are known as ionic bonds.

Recognizing Forces in Covalent Crystals

In covalent crystals (also known as network crystals), atoms are bonded together in an extensive network by covalent bonds, which are strong and directional bonds sharing electrons between atoms.

Key concepts

Molecular Crystals

Imagine a collection of tiny molecules neatly organized in a spacious ballroom – that's analogous to molecular crystals. These crystals are formed by individual molecules coming together and held in place by various intermolecular forces, which are akin to the gentle pushes and pulls dancers might use to position themselves on the dance floor. The weaker interactions such as London dispersion forces, or van der Waals forces, are the basic equivalent of casual glances or light touches - they occur due to momentary changes in electron density. Dipole-dipole interactions are a bit like dancers matching their movements to a partner’s, dependent on the positive and negative poles that create a somewhat stronger bond.

Hydrogen bonds, the strongest of these interactions, could be likened to holding hands – they occur when hydrogen atoms come close to electronegative atoms such as oxygen or nitrogen. This elegant dance of molecules in molecular crystals results in generally low melting and boiling points, as the forces are relatively easy to overcome with the addition of heat. These structures are common in organic compounds, like sugar or ice, and are significant in understanding biochemical processes.

Ionic Crystals

In the world of crystalline structures, ionic crystals are comparable to a highly structured and disciplined regiment of soldiers standing in a grid, each one positively or negatively charged and distinctly separated from the next by the space they occupy. This organized collection of ions is the result of electrostatic attraction, which pulls these oppositely charged ions together into a tight embrace, much like magnets snapping together. This attractive force, known as an ionic bond, is robust and dominates the crystal's properties.

The ionic crystals flaunt high melting and boiling points, indicating the strength of the bonds that hold them together. They are typically soluble in water and other polar solvents since these solvents can disrupt the ionic bonds, and they often conduct electricity when molten or dissolved due to the free-moving ions. Typical examples include table salt (sodium chloride) and many minerals.

Covalent Crystals

Covalent crystals, or network crystals, demonstrate the beauty of shared commitment, where each atom is connected to its neighbors by strong, covalent bonds. These bonds form by sharing electrons between atoms, creating a vast, interconnected network reminiscent of a spider's web, but on a microscopic scale. The covalent bonds exist in specific directions, which results in a highly ordered and rigid crystalline structure.

This interlocking creates exceptionally hard substances like diamonds, which boast remarkable stability and high melting points – a testament to the bond's strength. They generally do not conduct electricity, as the electrons are held tightly within the covalent bonds and aren't free to flow. Besides diamonds, silicon carbide and quartz are quintessential examples, used in various applications from industrial cutting tools to electronic components.