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Covalency - Definition, Covalent Bonding, Reason Behind Covalency, Practice Problems & FAQs

Covalency - Definition, Covalent Bonding, Reason Behind Covalency, Practice Problems & FAQs

Our parents always tell us that we should share our food, right?

But why is that?

By sharing the food we get to know each other and we form a mutual friendship and bond. So, sharing is always caring. This is a real-life example of sharing is caring, but did you know that our elements are also concerned about one another and form bonds with each other? Isn't it interesting?

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Let’s see how the elements present around us share this mutual relationship of sharing and caring with each other.

Table of Contents

  • Duplet and Octet Rule
  • Covalent Bonding
  • Definition of Covalency
  • Reason Behind Covalency
  • Practice Problems
  • Frequently Asked Questions - FAQs

Duplet and Octet Rule

There are different ways in which elements are bonded to each other in chemistry and one such process of bonding is known as covalency which we are going to discuss here. But before discussing covalency we should first talk about covalent bonding and the octet rule.

According to the octet rule, atoms are most stable when their valence shells contain eight electrons. Atoms lose, gain, or share electrons to achieve an inert gas configuration.

  • Noble gas atoms have little or no tendency to combine with each other or with atoms of other elements, according to research.
  • This implies that the electronic arrangement of these atoms must be stable.
  • Except for helium (following Duplet rule), which possesses two electrons (1s2) in its outermost shell, these elements (noble gases) have eight electrons (ns2np6) in their outermost shell.

The atoms having 8 electrons in their outermost shell are considered stable. Moreover, helium having 2 electrons in its outer shell is also considered stable.

Covalent Bonding

A shared pair of electrons from both participating atoms form a covalent connection. As a result of this electron pair sharing, the atoms will achieve stability in their outer shell, similar to noble gas atoms.

Atoms with high ionisation energy and low electron affinity find great difficulty losing or gaining electrons. As a result, such elements share electrons in order to establish a noble gas structure and stability and form a covalent bond. The covalent bond is a type of relationship that occurs when electrons are shared.

Covalent bonding can be accomplished in two ways:

  • By sharing electrons between atoms of the same kind (e.g. H2, Cl2 etc.).

  • By sharing electrons between atoms of different kinds (e.g. H2O etc.).

Properties of covalent bonding:

  • Covalently bound molecules do not conduct electricity because they lack free electrons.
  • In general, covalent compounds are not water-soluble.
  • The melting and boiling points of most covalently linked compounds are low.
  • Compounds with covalent bonds typically have a lower enthalpy of vaporisation and enthalpy of fusion.

Now that we have understood what covalent bonding is, let’s see what covalency is and how it is related to covalent bonding.

Definition of Covalency

Covalency is the process by which an element shares its electrons with another element (same or different) in order to achieve a stable electronic configuration.

When the chemical bonds are formed, the covalency of an atom is the number of electrons shared with the other atoms

In H2 molecule, for example, both hydrogen atoms will share one electron in order to achieve a stable electronic state, hence its covalency is one.

Types of covalent bonds and covalency:

Single covalent bond and covalency:

When two participating atoms share only one pair of electrons, they create a single bond. A single dash is used to indicate it (—). The development of a sigma bond (produced by the head-on overlapping of the orbitals which are hybrid along the bonding axis) will occur here.

H2 molecule, for example, has two hydrogen atoms that share one electron each, resulting in a noble gas arrangement. A single bond is created between two hydrogen atoms in this situation.

Here, both hydrogen atoms will share one electron in order to achieve a stable electronic state, hence its covalency is one.

Double covalent bond and covalency:

A double bond is formed when the two involved atoms share two pairs of electrons. Two dashes (=) are used to indicate it. The pi bond (produced by side-to-side overlapping of hybrid orbitals, above and below the bonding axis) will form in addition to the sigma bond.

For example, during the formation of the O2 molecule, both the oxygen atoms have six electrons in its valence shell. To complete its octet, each oxygen atom needs two extra electrons. As a result, the oxygen atoms share two pairs of electrons to form the oxygen molecule. Because they share two electron pairs, the two oxygen atoms create a double bond and hence its covalency will be 2.

Triple covalent bond and covalency:

A triple covalent bond is formed between the atoms when they share three pairs of electrons. To indicate the triple bond between the two atoms, three dashes (≡) are used. Among single, double, and triple bonds, the triple bond is the strongest.

Each nitrogen atom, for example, has five electrons in its valence shell. Each atom requires three extra electrons to complete its octet. As a result, the atoms combine to form the nitrogen molecule (N2) by sharing three electrons and forming a triple bond. Hence, its covalency is 3.

Reason Behind Covalency

An atom's octet is completed by the number of electrons it shares or accepts which brings stability to an atom. So, in simple terms, we can say that covalency takes place to bring stability to an atom.

Practice Problems

Q1: In covalency:

A. electrons are equally shared.
B. electrons of one atom are shared between two atoms.
C. electrons are transferred.
D. None of the above

Answer: (A)

Solution: When the chemical bonds are formed, the covalency of an atom is the number of electrons shared with the other atoms. The number of covalent bonds it creates with the other bonds is usually, but not always, the determining factor.

Carbon shares its four electrons with four electrons from four separate H atoms to form four covalent bonds in CH4. Hence, the covalency of carbon is four. In covalency, the electrons are equally shared.

So, we can say that option A is the correct answer.

Q2: Maximum covalency of oxygen is:

A. 1
B. 2
C. 3
D. 4

Answer: (B)

Solution: The maximum covalency of oxygen is 2. However, it also shows other valencies like 1 in peroxides, ½ in superoxides.

So, we can say that option B is the correct answer.

Q3: The covalency of nitrogen in ammonium ion is:

A. 1
B. 2
C. 3
D. 4

Answer: (D)

Solution: The nitrogen atom is linked to four hydrogen atoms in the ammonium ion (NH4+). The first three hydrogens are covalently connected to the nitrogen atom, while the fourth hydrogen is bonded by a coordinate bond.

So the nitrogen atom forms a total of four bonds. As a result, the covalency of the nitrogen atom is 4.

So, we can say that option D is the correct answer.

Q4: In covalency:

A. one atom acts as a donor and the other acts as an acceptor.
B. the electrons are shared by both the atoms.
C. electrons of one atom are shared between two atoms.
D. electrons are transferred.

Answer: (B)

Solution: A covalent bond is established between two atoms when two or more atoms share electrons to achieve a stable configuration that completes their octet and covalency is nothing but the process by which an element shares its electrons with another element in order to achieve a stable electronic configuration.

So, we can say the most appropriate answer is option D.

Frequently Asked Questions - FAQs

Question: What's the difference between valence electrons and valency?
Answer:
Valence electrons are the electrons in an atom's outermost shell. For example, nitrogen's electronic configuration is 1s22s22p3. So there are 5 valence electrons in the outermost shell.

The combining capacity of an atom, on the other hand, is referred to as valency.

Nitrogen, with an electronic configuration of 1s22s22p3, requires three more electrons to achieve a stable electronic configuration. We can say that it has a valency of 3 since it gains 3 electrons.

Question: What exactly is electronegativity?
Answer:
The tendency of an atom in a molecule to draw the shared pair of electrons towards itself is known as electronegativity.

Question: Is it possible for a chemical compound to have covalent and ionic bonds at the same time?
Answer:
Yes, a molecule can have both covalent and ionic bonds.

Take the example of sodium phosphate (Na3PO4). Because sodium is a metal and the phosphate ion (PO43-) is a polyatomic anion, Na3PO4 is an ionic compound. However, this phosphate ion (PO43-) is held together by a covalent link, whereas an ionic bond is formed between Na+ and PO43- ions. As a result, we can say that this chemical has both ionic and covalent bonds in it.

Question: What is the covalency of fluorine?
Answer:
Fluorine has 7 valence electrons. The fluorine atom shares one electron with the other fluorine atom to produce F2. It can also share one electron with the hydrogen atom to form HF, by completing its octet. Hence, its covalency is 1.

Question: Why does nitrogen show the highest covalency of 4?
Answer:
Because of the absence of d orbitals in its valence shell, nitrogen shows a covalency of 4 which is maximum. In its valence shell, only four orbitals are available (one 2s and three 2p orbitals).

Question: What's the difference between electrovalency and covalency?
Answer:
The number of electrons lost or acquired by an atom to create ionic bonds is known as electrovalency. Whereas, the number of electrons shared by atoms to create a covalent connection is known as covalency. The creation of ionic bonding is explained by electrovalency.

 

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