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Covalent Compounds

Covalent compounds are basically the individually molecules having bonds which are very strong as the atoms within the covalent molecules are held very tightly together. Each molecule tends to be quite separate and attractions between the individual molecules in a covalent compounds tends to be small.

The weak attractive forces between the molecules or weak intermolecular forces along with the absence of overall electric charge results in relatively little energy required for separating them. These are some of the facts that we will be discussing in this page.

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What is a Covalent Compound?

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Covalent compounds which are mostly individual gaseous molecules at room temperature and pressure or liquids with low relatively low boiling points have weak intermolecular forces which hold these atoms together. Many covalent compounds are solids with low melting points but small number of these have a completely different structure. They form giant structures where huge number of atoms are held together as they are held together by shared electrons.

These giant molecular structures are basically lattices made up of molecules which are held together by covalent bonds structure. These covalent bonds are very strong and tend to be very hard with a high melting points which are different from most of the covalent compounds. Examples are diamond and graphite of carbon atom network and silica of silicon and oxygen atoms network.

Covalent Compounds Definition

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Compounds which are held together by covalent bonding (by sharing of electrons) are better known as covalent compounds. These are basically molecules made mainly of non-metals which are made up by sharing electrons and held together by van der Waal forces.

General Properties of Covalent Compounds

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The properties of covalent compounds are based mainly on the structure these molecules are made up of. The melting points of molecules like diamond on heating up to 4198 K changes straight into a gas whereas ionic salts like NaCl melts at 1074 K which is much lower in temperature.

Solids melt when their lattice break down and molecules like diamond requires huge amount of heat energy to break down the carbon atoms lattice. In case of ionic solids the bonded atoms are held together by electrostatic forces which are ions in an ionic lattice held together by oppositely charged particles.
  • Covalent compounds usually have low melting points except in case of molecules like diamonds and silica lattice
  • The boiling points of these covalent molecules is low as the force of attraction between the bonded atoms are held together by van der Waal forces
  • Covalent bonded compounds are usually gases and liquids with low boiling and melting points
  • Covalent compounds which are solids are either have soft structures like graphite as there is a cloud of electrons in between each layer of carbons
  • The covalent compounds are non-conductors of electrical charge as there are no charged ions in covalent molecules except in case of graphite where we get to see cloud of electrons which help in the conduction
  • Covalent compounds are bad conductors of heat energy as well, as these molecules lack free electrons which eventually provides infinite resistance to flow of heat energy.
  • Conduction of heat does not bring in any changes in metals as they have free electrons to carry these energy but in case of covalent compounds these result in complete combustion as the molecules do not allow free passage of either electrical charge and heat energy and hence bring in the chemical change
  • Covalent compounds do not possess polar characteristics as a general property and hence are not soluble in water. Water molecules are not absolutely neutral and have a slight negative charge on the oxygen atom and slight positive charges on the hydrogen atoms and since covalent compounds are made up of neutral molecules or molecules with slight charges and hence are not attracted to water molecules strongly.

List of Covalent Compounds

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Covalent compounds are as follows:

Covalent compounds are mainly made up of non-metals and in some cases the metalloids.

The list of covalent compounds are huge and almost every second material that we see around us is either derived directly from the living world or is derived in some way from the non-metals. These covalent compounds are either derived from organic or inorganic stream.
Inorganic covalent compounds:

Hydrogen chloride $(HCl)$, Carbon dioxide $(CO_{2})$, Sulphur dioxide $(SO_{2})$, Carbon monoxide $(CO)$, Hydrogen sulphide $(H_{2}S)$, Hydrogen peroxide $(H_{2}O_{2})$, Hydrogen fluoride $(HF)$, Hydrogen bromide $(HBr)$ etc.

Organic covalent compounds:

Acetic acid $(CH_{3}COOH)$, Methane $(CH_{4})$, Ethane $(C_{2}H_{6})$, Ethanol $(CH_{3}CH_{2}OH)$, Ethanal $(CH_{3}CHO)$, benzene $(C_{6}H_{6})$ etc.

Physical Properties of Covalent Compound 

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  • Covalent compounds which are liquid evaporate which means that molecules of liquids and solids loses from their surface into air. The more these liquids can break out from liquid or solid, the faster the evaporation can occur.
  • Covalent compounds have very less affinity between their molecules but have strong bonds within their own molecules.
  • Various covalent compounds have their own characteristically shaped molecules with bonds directed at pre-set angles.
  • Some of the covalent molecules have shapes which stuck to our nerve endings of our nose and produce electrical signal in our brain cells. The various perfumes and all other scented products have covalent molecules that produce characteristic smells and so does the bad smelling products.
  • Covalent compounds are generally insoluble in water as we could see that even after drenching in rain we do not melt down. Our skin and other cell materials are made up of proteins, oils and fats.
  • Some of the covalent compounds especially medicines are water soluble while the rest are oil soluble.
  • All covalent bonds have own characteristic bond angles which and these influence the shape of any covalent molecule. These molecules can twist freely in any single bond but in case they have double bonds the twist about the central overlap is restricted.
  • Most of the covalent compounds are non-polar or have very little tendency to split completely to form ions and hence never conduct electricity. But there are some covalent molecules that have groups within them which allows partial ion formation like in case of acetic acid. This small amount of H+ ion gives the acetic acid or vinegar the sharp taste.

Characteristics of Covalent Compounds

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The covalent bonds are basically bonding between atoms and not between ions. The main characteristics of the covalent compounds are as follows:
  • At normal temperature and pressure the covalent compounds are generally either liquid or gases but there are solids as well which have higher molecular weights
  • The covalent compounds crystals are of two types with weak van der Waal force holding these together like in Iodine which are easily fusible and volatile, and the other with large network of atoms setting up the macro molecules
  • Insoluble in polar solvents like water but soluble in organic solvents like ether and benzene
  • Covalent bonds are directional in nature and hence the isomerism phenomenon is exhibited in covalent compounds
  • Covalent compounds exist as molecules which are held together by van der Waal forces, exhibit low melting and boiling points
  • Covalent compounds do not dissociate into ions in solutions and hence are non-conductors of electricity
  • The rate of reactions of most covalent compounds are slow.
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