Ionic and Covalent Bond

An Introduction to Bonds: Ionic and Covalent

There are various kinds of chemical forces and bonds that tie up molecules with each other. The two fundamental kinds of bonds are marked as ionic bond and covalent bond. Ionic bonds need a minimum of one electron acceptor and one electron donor. On the other hand, in covalent bonds, atoms which have similar electronegativity share electrons because none of the atoms repel or attract the shared electrons.

In the following section, you will get to know about the ionic and covalent bond in detail. You will also understand the difference b/w ionic and covalent bond and why ionic bonds have a partially covalent character.

Introduction to Ionic Bonding

Ionic bonding refers to the entire shift of valence electron(s) in between the atoms. It is a kind of chemical bond which yields two ions that are oppositely charged. In this bonding, a metal element becomes a cation (+vely charged ion) by dropping electrons, while a non-metal element becomes an anion (-vely charged ion) by accepting those electrons. Ionic bonds need an electron donor such as a metal, along with an electron receiver such as a non-metal.

Ionic bonding is seen as the outermost orbitals of metals, containing few numbers of electrons. As they lose electrons, the metals can attain configuration of a noble gas and octet rule gets satisfied. In the same manner, non-metals whose valence shells have near to eight electrons, easily receive the electrons to attain noble gas configuration. Here, for the octet rule to get satisfied, donation and acceptance of more than one electron can take place. The positive and negative charges on cation and anion respectively are equal to the number of electrons accepted or donated. Also, the net charge of the compounds in this bonding has to be zero.[Table]

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The sodium molecule in the above figure gives out the lone electron in its outermost orbital to attain octet configuration. Hence, it forms a cation (+vely charged ion) because of its electron loss.

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The atom of chlorine here accepts one electron to attain its octet configuration, which forms an anion (-vely charged ion).

The overall energy predicted for the process of ionic bonding that includes electron affinity of non-metal and ionisation energy of metal is normally positive. This indicates that the undergoing reaction is unfavourable and endothermic. However, the reaction is extremely favourable because the particles have an electrostatic attraction in between them. At an ideal interatomic distance, as the particles attract each other, it releases ample energy to ease the reaction. Maximum ionic compounds being polar, they tend to split up in polar solvents. The reason for this phenomenon is because of the presence of opposite charges.

Note: Size effect in ionic bond adds to the lattice energy of ionic solids, and hence determines their solubility in water.

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The example above shows that the sodium atom gives out its one valence electron to the atom of chlorine. This leads to the formation of one sodium and one chlorine cation and anion, respectively. Note that the resulting compound’s charge is zero.

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With regards to this example, the atom of magnesium donates both the valence electrons to atoms of chlorine. The chlorine atoms can accept one electron each to attain noble gas configuration. So, two chlorine atoms are needed that will accept two electrons of magnesium. Here also, the net charge is zero.

Next, let us proceed with covalent bonds.

Introduction to Covalent Bonding

Covalent bonding deals with electron sharing between atoms, and this kind of a bond takes place between elements that are close to one another in periodic table or two atoms of a similar element. Covalent bonds majorly occur between non-metals, but it is seen between metals and non-metals too.

When atoms have same electronegativity, this bonding tends to occur as both the atoms have similar electron affinity and none of them tend to give out electrons. The atoms share electrons to attain octet configuration and stabilise even more. Moreover, as electron affinity is very less and ionisation energy is very high, ionic bond cannot occur. For instance, ionic bonding does not occur in carbon as it holds four electrons in its outermost shell, which is half of the octet.

For ionic bonding to occur, carbon molecules will have to lose or gain four electrons. As this is extremely unfavourable, molecules of carbon share their valence electrons across single, double and triple bonds to attain noble gas configuration for each atom. Covalent bonding consists of interactions of pi and sigma orbitals, and hence it results in single, double, triple and quadruple bond formations.

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Here, one atom of phosphorus shares its three unpaired electrons to the three atoms of chlorine. In the final product, all four molecules hold eight valence electrons and octet rule gets satisfied.

By now, you must have understood what ionic and covalent bonds are. However, it is also said that ionic bonds have covalent character. This was first explained by Kazimierz Fajans in the year 1923.

Fajans’ Rule: Covalent Character in Ionic Compounds

Though an atomic bond like M+ X- is 100 per cent ionic, it has characteristics of a covalent bond. As stated by Fajans, if two ions which are oppositely charged are brought together, the bond nature between them entirely depends on the effect of one ion on another. When two ions A+ and B- are brought together, the positively charged ion gets attracted to the valence electron of the anion and repulsion occurs with the +vely charged nucleus. As a result, it leads to distortion, polarisation and deformation of the anion. Ionic bonds occur when ionisation is small, whereas covalent bond takes place when polarisation degree is high.

Therefore, an ion’s power to distort another ion is called its polarisation power and its tendency to become polarised by another ion is called polarisability.

Following are the factors that favour covalent character in ionic bonds. 

  • Small Cation (Positively Charged Ion)

Due to a high positive charge concentration on a small space, the smaller cation holds large power of polarisation. This illustrates why lithium chloride (LiCl) has a more covalent character than potassium chloride (KCl).

  • Large Anion (Negatively Charged Ion)

When the anion is huge, polarisability also becomes higher, which refers to vulnerability to get polarised. This is because the valence electrons of a huge anion are loosely packed, and as a result, they can be feasibly withdrawn by the cation. An example of this scenario is why iodides are covalent among halides.

  • High Charge on Any One Ion

Due to the increase of ion charge, cation’s electrostatic attraction of the anion’s valence electron also increases, and hence the formation of covalent bond increases. It takes place in the order like Na+, Cl, Mg2+, (Cl2)2-, Al3+, (Cl3)3-

  • Cation’s Electronic Configuration

Among the two ions which have the same charge and size, one having eighteen electrons in valence shell (pseudo noble gas configuration) and a cation having eight electrons in valence shell (noble gas configuration), the former is more polarising. Therefore, CuCl is much more covalent than NaCl, though they have similar size and charge (Cu+ ion: 0.96A°, Na+ ion: 0.95A°).

In a simpler way, Fajan’s rule can be summed up as:

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Difference between Ionic and Covalent Bonding

Here is a tabular representation of ionic bond vs covalent bond:

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Do It Yourself

1. Ionic bonds occur between which elements?

a) metal and metal b) metal and non-metal c) non-metal and non-metal d) none

2. Chlorine requires how many electrons to have full outer configuration?

a) 1 b) 0 c) 8 d) 7

3. According to Fajans’ rule, when do ionic bonds occur?

a) ionisation is huge b) polarisation is high c) ionisation is small d) none of these

The above discussion must have cleared your concepts related to ionic bond and covalent bond and why the former is partially covalent. If you wish to know more concepts such Chemistry concepts, download our Vedantu app today to access a wide range of study materials and online tutorials.

FAQ (Frequently Asked Questions)

1. How to Determine Whether a Bond is Covalent or Ionic?

Ans. There are few ways by which one can say whether a bond is an ionic bond or covalent. According to the definition, metal and non-metal have an ionic bond, while preferably two non-metals have a covalent bond. So, by looking at the periodic table, one can determine whether a compound is formed from bonding of metal and non-metal or two non-metals.

2. Which Bond is Stronger between an Ionic Bond and Covalent Bond, and Why?

Ans. Ionic bonds are much stronger than covalent bonds. The reason is because of the presence of coulombic attraction between oppositely charged ions.

3. What are the Examples of Covalent Bonding?

Ans. Some examples of covalent bonds are water, vulcanised rubber and diamonds.

4. What is the Similarity between the Ionic Bond and Covalent Bond?

Ans. The basic similarity between these two bonds is that their result is similar. Both these bonds lead to the formation of stable molecules.