Characteristics and Properties of Covalent Compounds

A covalent molecular compound consists of individual molecules that contain only covalent bonds. The covalent bonds within the molecules are very strong and highly directional, so the molecules usually have definite shapes and retain their identities during physical changes. The forces between the molecules are by comparison very weak. It's these weak intermolecular forces that determine many of the properties of covalent molecular compounds.

Elemental Composition of Covalent Compounds. Compounds that contain both metals and nonmetals are usually ionic, not covalent. So KBr and Na2SO4 are easily recognized as ionic compounds; CO2 and CH4 are covalent. You have to watch for a few exceptions when using this rule of thumb. NH4Cl is an ionic compound, not a covalent one, because the NH4+ (ammonium) ion is combined with a chloride ion.

Properties of Covalent Molecular Compounds.

 The general characteristics of covalent compounds are as follows;

(i).     Gases, Liquids or Solids at Room Temperature

        The covalent compounds are often gases, liquids or relatively soft solids under ordinary conditions. This is because of weak intermolecular forces between the molecules.

(ii).    Low Melting Points

        Covalent compounds have generally low melting points (or boiling points). The molecules are held together in the solid crystal lattice by weak forces. On application of heat, the weak forces are easily broken down and hence these compounds have low melting and boiling points.

(iii).    Neither Hard nor Brittle

        While the ionic compounds are hard and brittle, covalent compounds are neither hard nor brittle. There are weak forces holding the molecules in the solid crystal lattice. A molecular layer in the crystal easily slips over the adjacent layers. Thus the crystals are easily broken and there is no sharp cleavage between the layers on application of external force.

(iv).     Soluble in Organic Solvents

        In general, covalent compounds dissolve readily in non polar organic solvents (benzene, ether). The kinetic energy of the solvent molecules easily overcomes the weak intermolecular forces. Covalent compounds are insoluble in water. Some of them (alcohols, amines) dissolve in water due to hydrogen bonding.

(v).    Non-Conductors of Electricity

        Since there are no cations or anions in covalent molecules, the covalent compounds in the molten or solution form are incapable of conducting electricity.

(vi).    Exhibit Isomerism

        Covalent bonds are rigid and directional, the atoms being held together by shared electron pair and not by electrical lines of force. This gives opportunity for various spatial arrangements and covalent compounds exhibit stereo-isomerism.

(vii).    Molecular Reactions

        The covalent compounds don't have ions and hence these reactions are slow.