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Ionic Bond - Partially Covalent in Nature

Ionic Bond - Partially Covalent in Nature

Shivani PooniaUpdated on 02 Jul 2025, 06:20 PM IST

If the atoms that form a covalent bond are identical, as in H2, Cl2, and other diatomic molecules, then the electrons in the bond must be shared equally. We refer to this as a pure covalent bond. Electrons shared in pure covalent bonds have an equal probability of being near each nucleus.

In the case of Cl2

Ionic Bond - Partially Covalent in Nature
Ionic Bond - Partially Covalent in Nature

Each atom starts with seven valence electrons, and each Cl shares one electron with the other, forming one covalent bond:

Cl+Cl⟶Cl2

When the atoms linked by a covalent bond are different, the bonding electrons are shared, but no longer equally. Instead, the bonding electrons are more attracted to one atom than the other, giving rise to a shift of electron density toward that atom. This unequal distribution of electrons is known as a polar covalent bond, characterized by a partial positive charge on one atom and a partial negative charge on the other. The atom that attracts the electrons more strongly acquires the partial negative charge and vice versa.

For example, the electrons in the H–Cl bond of a hydrogen chloride molecule are shifted towards chlorine. Thus, in an HCl molecule, the chlorine atom carries a partial negative charge and the hydrogen atom has a partial positive charge as shown in the figure given below.

Two diagrams are shown and labeled “a” and “b.” Diagram a shows a small sphere labeled, “H” and a larger sphere labeled, “C l” that overlap slightly. Both spheres have a small dot in the center. Diagram b shows an H bonded to a C l with a single bond. A dipole and a positive sign are written above the H and a dipole and negative sign are written above the C l. An arrow points toward the C l with a plus sign on the end furthest from the arrow’s head near the H.

(a) The distribution of electron density in the HCl molecule is uneven. The electron density is greater around the chlorine nucleus. (b) Symbols δ+ and δ– indicate the polarity of the H–Cl bond.

When the electronegativity difference is very small or zero, the bond is covalent and nonpolar. When it is large, the bond is polar covalent, or ionic. The absolute values of the electronegativity differences between the atoms in the bonds H–H, H–Cl, and Na–Cl are 0 (nonpolar), 0.9 (polar covalent), and 2.1 (ionic), respectively. The degree to which electrons are shared between atoms varies from completely equal (pure covalent bonding) to not at all (ionic bonding). The figure below shows the relationship between electronegativity difference and bond type.

Two flow charts and table are shown. The first flow chart is labeled, “Electronegativity difference between bonding atoms.” Below this label are three rounded text bubbles, connected by a downward-facing arrow, labeled, “Zero,” “Intermediate,” and “Large,” respectively. The second flow chart is labeled, “Bond type.” Below this label are three rounded text bubbles, connected by a downward-facing arrow, labeled, “Pure covalent,” “Polar covalent,” and “Ionic,” respectively. A double ended arrow is written vertically to the right of the flow charts and labeled, “Covalent character decreases; ionic character increases.” The table is made up of two columns and four rows. The header line is labeled “Bond type” and “Electronegativity difference.” The left column contains the phrases “Pure covalent,” “Polar covalent,” and “Ionic,” while the right column contains the values “less than 0.4,” “between 0.4 and 1.8,” and “greater than 1.8.”

As the electronegativity difference increases between two atoms, the bond becomes more ionic.

Recommended topic video on (Ionic character in covalent bond)

Some Solved Examples

Example 1: The values of electronegativity of atoms A and B are 1.80 and 4.0 respectively. The percentage of ionic character of the A-B bond is?

1)43.14%

2)50 %

3)55.3 %

4) 52.14 %

Solution

As we learn
Percent ionic character = 16 (XB-XA) + 3.5 (XB-XA)2

Where XB is the electronegativity of atom B and XA is the electronegativity of A

So, Percent ionic character = 16 (4-1.8) + 3.5 (4-1.8)2

= 16 X (2.2) + 3.5 X (2.2)2

= 35.2 + 16.94

= 52.14

Hence, the answer is the option (4).

Example 2: The electronegativities of F, Cl, BrF,Cl, Br and II are 4.0, 3.0, 2.8 4.0,3.0,2.8 and 2.5 respectively.Hydrogen halide with a high percentage of ionic character is

1)HFHF
2) HCl
3) HBr
4) HI

Solution

Ionic Character in Covalent Bond -

When the electronegativity difference is very small or zero, the bond is covalent and nonpolar. When it is large, the bond is polar covalent or ionic. The absolute values of the electronegativity differences between the atoms in the bonds H–H, H–Cl, and Na–Cl are 0 (nonpolar), 0.9 (polar covalent), and 2.1 (ionic), respectively. The degree to which electrons are shared between atoms varies from completely equal (pure covalent bonding) to not at all (ionic bonding). The figure below shows the relationship between electronegativity difference and bond type.

As the electronegativity difference increases between two atoms, the bond becomes more ionic.

The greater the electronegativity difference more is the ionic character. Thus, H-F has maximum ionic character.
Hence, option number (1) is correct.

Example 3: If the molecule of HCl were polar, the expected value of dipole moment is 6.12 D(debye) but the experimental value of dipole moment was 1.03D. The percentage ionic character is:

1) 17

2)83

3)50

4)Zero

Solution

The percentage ionic character is given by the following formula

$\%$ Ionic Character $=\frac{\text { experimental value of dipole moment }}{\text { theoretical value of dipole moment }} \times 100=\frac{1.03 \mathrm{D}}{6.12 \mathrm{D}} \times 100=16.83 \%=17 \%$ Hence, the answer is the option (1).

Example 4: Bond distance in HF is 9.17×10−11m′ 9.17×10−11m′ Dipole moment of HF is 6.104×10−30 cm2 6.104×10−30 cm2The percent ionic character in HF will be :

(electron charge ==1.60×10−19C)=1.60×10−19C))

1)61.1%
2)38.0%
3)35.5%
4)41.5%

Solution

$\begin{aligned} & \text { Given, } e=1.60 \times 10^{-19} \mathrm{C}, \mathrm{d}=9.17 \times 10^{-11} \mathrm{~m} \text { From } \\ & \quad \mu=e \times d \mu=1.60 \times 10^{-19} \times 9.17 \times 10^{-11}=14.672 \times 10^{-30} \\ & \% \text { ionic character }=\frac{\text { Observed dipole moment }}{\text { Dipole moment for 100 }}=41.5 \%\end{aligned}$

Hence, the answer is the option (4).

Example 5: Which of the following is the most ionic?

1)P4O10

2) MnO

3)CrO3

4)Mn2O7

Solution

Magnitude of positive charge α polarization power

α covalent character

α 1/ ionic character

If the magnitude positive charge is high then it will be very unstable to remain as an ion because it needs an electron to get stable that's why it makes a covalent bond at a high magnitude positive charge. magnitude positive charge

P4O10 P = +5

MnO Mn = +2

CrO3 Cr = + 6

Mn2O7 Mn = + 7

Among them, MnO has the lowest magnitude of positive charge. Hence, MnO is the most ionic compound.

Hence, the answer is the option (2).

Summary

When the bond is formed between two positively charged atoms is called ionic bond the force that joined these bonds is the electrostatic force of attraction.

Frequently Asked Questions (FAQs)

Q: How does the concept of electronegativity equalization relate to the partial covalent nature of ionic bonds in complex molecules or crystals?
A:
In complex molecules or crystals, electronegativity equalization can lead to charge redistribution across the entire structure. This process can result in bonds with varying degrees of covalent character, even in predominantly ionic systems, affecting overall properties and reactivity.
Q: What is the significance of bond polarity in understanding the partial covalent nature of ionic bonds?
A:
Bond polarity provides a measure of charge separation in a bond. In partially covalent ionic bonds, the polarity is often less extreme than in purely ionic bonds, reflecting the shared electron density and incomplete charge transfer.
Q: How does the partial covalent nature of ionic bonds affect their behavior in electrochemical processes?
A:
The partial covalent nature can influence electrochemical properties such as redox potentials, electrode kinetics, and ion transport. Compounds with significant covalent character may show different electrochemical behavior compared to purely ionic systems.
Q: What is the role of electron correlation energy in the partial covalent nature of ionic bonds?
A:
Electron correlation energy, arising from the interactions between electrons, contributes to the stability of partially covalent ionic bonds. It can lead to deviations from simple electrostatic models and affect the overall bonding characteristics.
Q: How does the partial covalent nature of ionic bonds affect their behavior in solid-state reactions?
A:
The partial covalent nature can influence solid-state reaction mechanisms, diffusion processes, and phase transitions. Compounds with significant covalent character may exhibit different reactivity patterns and kinetics compared to purely ionic systems.
Q: What is the significance of bond length in understanding the partial covalent nature of ionic bonds?
A:
Bond lengths in partially covalent ionic compounds often deviate from those expected for purely ionic interactions. Shorter bond lengths than predicted by ionic radii can indicate increased covalent character due to electron sharing.
Q: How does the concept of electron density distribution relate to the partial covalent nature of ionic bonds?
A:
Electron density distribution in partially covalent ionic bonds shows characteristics of both ionic and covalent bonding. Analysis of this distribution through techniques like X-ray diffraction can provide insights into the degree of covalent character.
Q: What is the role of molecular orbital theory in explaining the partial covalent nature of ionic bonds?
A:
Molecular orbital theory can describe the partial covalent nature of ionic bonds by showing the formation of bonding and antibonding orbitals. This approach provides a more nuanced view of electron distribution compared to simple ionic models.
Q: What is the significance of bond dissociation energy in compounds with partially covalent ionic bonds?
A:
Bond dissociation energies in partially covalent ionic compounds are often higher than expected for purely ionic interactions. This increased energy reflects the additional stabilization provided by the covalent component of the bond.
Q: How does the concept of electron affinity difference relate to the partial covalent nature of ionic bonds?
A:
The difference in electron affinities between bonding atoms affects the degree of electron transfer and sharing. Smaller differences can lead to more covalent character, while larger differences tend to result in more ionic bonding.
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