Covalent Crystals also called atomic crystals are the molecular solids in
which the same or different atoms are joined together by covalent
bonding. Atoms of the same or different kinds with no/small changes in
electronegativity form the structural units of such crystals
Unlike Ionic crystals, Covalent bonds are directional in nature. The
continuous networks of atoms in the lattice form a connection that binds
the entire crystal together as a single big molecule.
Some of the examples of covalent crystals are diamond, graphite, silicon dioxide,
and so on.
It is composed of carbon atoms that have been sp3 hybridized. Each
carbon atom is connected to four other carbon atoms in a tetrahedral
array to build a massive network of carbon rings with six members. In
other words, the unit cell of the diamond is a face-centered cubic array
of carbon atoms with four extra carbon atoms inserted into four
tetrahedral holes. As the crystal is closed packed arranged in a threedimensional lattice, it possesses a high density and refractive index and
is, therefore, the hardest substance.
Some of the examples of covalent crystals are diamond, graphite, silicon dioxide,
and so on.
It is made up of layers of fused six-membered rings of
sp2 hybridized carbon atoms, with each carbon
bound to three others, and atoms arranged in
alternate layers of graphite. Every other carbon atom
in one layer is directly under/above the center of a
six-membered ring in an adjacent layer and hence
forms the staggered layers.
• Melting and Boiling point: As the atoms are held together by the covalent bonding
via sharing of electron between atoms, it posseses strong forces, and hence high
amounnt of energy is required to break this bond. Thus, Covalent crystals have
high melting and boiling point.
• Hardness: Because of the directional properties of the covalent bonds, the atoms
are strongly bounded in the lattice and cannot be easily displaced or compressed.
This is the reason for the hardness of covalent crystals.
• Solubility: Covalent crystals are insoluble in polar solvent, but soluble in non-polar
solvent.
• Conductivity: Since the electrons are tightly held by the atoms and cannot move
through the lattice, covalent crystals possesses poor electrical conductivity.
• Brittleness: When a crystal is subjected to sufficient force, covalent bonds are
broken as the lattice is distorted, and as a result of which shattering occurs in the
crystal. Thus, covalent crytals like diamond are highly brittle in nature.