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What are Covalent Compounds? Definition, Formation, Properties

  • Difficulty Level : Hard
  • Last Updated : 09 Nov, 2021

Pure substances exist in two forms: elements and compounds. Elements are the simplest chemical substances in which all of the atoms are the same. Compounds are chemical substances composed of two or more elements chemically bound together in a specific ratio.

When two or more elements combine chemically in a fixed mass ratio, the resulting product is known as a compound. 

When the elements combine, some of their individual properties are lost, and the newly formed compound has new properties. Chemical formulas are used to represent compounds. A chemical formula is a symbolic representation of the atom proportions that make up a specific chemical compound. Water’s chemical formula is H2O, which indicates that two hydrogen atoms and one oxygen atom have combined to form one molecule of H2O. Common salt has the chemical formula NaCl, which shows that one atom of sodium and one atom of chlorine combine to form one molecule of NaCl.

Chemical compounds are classified into two types: covalent compounds and ionic compounds. Ionic compounds are composed of electrically charged atoms or molecules as a result of electron gain or loss. Ionic compounds are formed when oppositely charged ions react with one another, most commonly when a metal reacts with a nonmetal. Covalent, or molecular, compounds are formed when two nonmetals react with one another. By sharing electrons, the elements combine to form a compound, resulting in an electrically neutral molecule. 

Covalent Compounds

Gilbert N. Lewis, an American physical chemist, first described covalent bonding in a 1916 article, though he did not use the term. In a 1919 article in the Journal of the American Chemical Society, American chemist Irving Langmuir used the term covalence in reference to bonding for the first time.

Electrons are shared between atoms in covalent compounds. Because electrons are shared, they have distinct physical properties such as lower melting points and electrical conductivity when compared to ionic compounds.

The sharing of electrons between two or more atoms is what defines covalent bonds. These bonds are most commonly found between nonmetals or between two elements of the same element. Two atoms with similar electronegativity will not exchange an electron from their outermost shell; instead, the atoms will share electrons to fill their valence electron shell. Covalent compounds are formed when the electronegativity values of the elements in a compound are identical or similar. As a general rule, atoms form covalent bonds if the electronegativity difference is less than 2 on the Pauling scale. If the difference in electronegativity is greater than two, the elements form ionic bonds. An example is CO2.

An exception to the above rule: In general, if a molecule is entirely composed of nonmetals, it is a covalent compound. There is, however, one notable exception. Because the ammonium cation (NH4+) is so electropositive, it forms ionic bonds rather than covalent bonds with nonmetals. At the same time, the nitrogen and hydrogen atoms have covalent bonds. Ammonium chloride (NH4Cl) and ammonium nitrate (NH4NO3), for example, contain both ionic and covalent bonds.

Properties of Covalent Compounds

  1. The covalent compounds show low melting and boiling points.
  2. They are inefficient electrical and thermal conductors.
  3. Brittle or soft solids.
  4. Fusion enthalpies are low
  5. Low vaporization enthalpies
  6. Covalent compounds can exist as a solid, a liquid, or a gas at room temperature and normal atmospheric pressure, whereas ionic compounds can only exist as solids.
  7. Although there are no free mobile ions or electrons in solid ionic compounds, ionic compounds dissolved in water form an electrically conductive solution. Covalent compounds, on the other hand, have no electrical conductivity, whether in their pure form or when dissolved in water.
  8. Ionic compounds have crystalline structures that are stable. As a result, they have higher melting and boiling points than covalent compounds.

Formation of Covalent Compounds

An atom consists of a positively charged nucleus and negatively charged electrons that surround it. Consider two chlorine atoms, each of which has seven valence electrons. Each of these chlorine atoms only requires one more valence electron to finish its outer shell. The atoms form a single bond by sharing two electrons. These electrons are concentrated in the space between the two chlorine atoms, held in place by magnetic attraction. Negative electrons are attracted to each atom’s positively charged nucleus, preventing the atoms from separating.

The bonded electrons between two chlorine atoms are shared evenly – each atom pulls on the shared electrons in the same way. However, this is not always the case because some atoms are more electronegative than others. The ability of an atom to attract electrons is referred to as electronegativity. If a covalent bond is formed between one atom that is truly electronegative and another that is not, the electrons in the bond will not be distributed evenly. Uneven sharing causes the formation of a dipole, which is the separation of charges between two covalently bonded atoms.

Hydrogen fluoride is an example of a dipole-containing simple covalent compound. In comparison to hydrogen, the fluorine atom is extremely electronegative. Since the shared electrons spend the majority of their time swarming the fluorine atom, the charge distribution is uneven. Fluorine has a partial negative charge in this image, while hydrogen has a partial positive charge.

Sample Questions

Question 1: Why do atoms react and how?

Answer:

Atoms with eight electrons in their final orbit are stable and do not react. Atoms with fewer than eight electrons react with other atoms to gain eight electrons in their outermost orbit and thus become stable. Atoms with slightly more than eight electrons may lose them to atoms with fewer than eight. Atoms that cannot lose or gain may share to obtain an octet configuration. Even after the reaction, molecules lacking an octet configuration may accept a lone pair of electrons from other atoms or molecules.

Question 3: What are hybridized orbitals?

Answer:

Relatively similar energy sub-orbitals can merge to form a new set of the same number of orbitals, with the property of all contributing orbitals being proportional to their numbers. These orbitals are called hybridised orbitals.

Question 4: What is the classification of compounds?

Answer:

Compounds are classified into two basic groups based on how the atoms in the compound bind to one another. These two types are known as molecular and salt compounds.

Question 4: What is the difference between an element a compound and a mixture?

Answer:

A material made up of only one type of atom. A compound is a material made up of more than one type of bonded atom. A mixture is a mixture of two or more unbounded components or compounds, each of which retains its own properties.

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