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Chemical Bonding and Molecular Structure - Ionic or Electrovalent Bond

Grade 11CBSEChemistry

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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An ionic or electrovalent bond is formed by the complete transfer of one or more electrons from one atom to another, resulting in the formation of cations and anions held together by strong electrostatic forces.

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The formation of an ionic bond is favored by low ionization enthalpy of the metal, high negative electron gain enthalpy of the non-metal, and high lattice enthalpy of the resulting compound.

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Lattice Enthalpy (ΔlatticeH⊖\Delta_{lattice}H^{\ominus}) is the energy required to completely separate one mole of a solid ionic compound into its constituent gaseous ions.

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According to the Octet Rule, atoms tend to lose, gain, or share electrons to achieve a stable electronic configuration of the nearest noble gas (ns2np6ns^2 np^6).

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Ionic compounds generally have high melting and boiling points, are soluble in polar solvents like H2OH_2O, and conduct electricity in molten or aqueous states due to the presence of free ions.

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The crystal structure of an ionic compound depends on the packing of ions, which is influenced by the size of the ions and the magnitude of their charges.

📐Formulae

F=kq1q2r2F = k \frac{q_1 q_2}{r^2}

U∝∣z+z−∣r++r−U \propto \frac{|z^+ z^-|}{r_+ + r_-}

ΔfH⊖=ΔsubH+12ΔbondH+IE+ΔegH+U\Delta_f H^{\ominus} = \Delta_{sub} H + \frac{1}{2}\Delta_{bond} H + IE + \Delta_{eg} H + U

Electrovalency=Number of electrons lost or gained by an atom\text{Electrovalency} = \text{Number of electrons lost or gained by an atom}

💡Examples

Problem 1:

Explain the formation of Magnesium Chloride (MgCl2MgCl_2) using Lewis electron dot structures.

Solution:

Mg→Mg2++2e−Mg \rightarrow Mg^{2+} + 2e^- and 2Cl+2e−→2Cl−2Cl + 2e^- \rightarrow 2Cl^-. The resulting ions attract to form Mg2+[Cl]2−Mg^{2+}[Cl]^-_{2}.

Explanation:

Magnesium has the configuration [Ne]3s2[Ne] 3s^2. It loses two electrons to achieve the stable [Ne][Ne] configuration. Each Chlorine atom ([Ne]3s23p5[Ne] 3s^2 3p^5) gains one electron to complete its octet, resulting in the formation of MgCl2MgCl_2.

Problem 2:

Between NaClNaCl and MgOMgO, which compound is expected to have a higher lattice enthalpy and why?

Solution:

MgOMgO has a higher lattice enthalpy than NaClNaCl.

Explanation:

Lattice enthalpy is directly proportional to the product of the charges of the ions (U∝∣z+z−∣U \propto |z^+ z^-|). In MgOMgO, the charges are +2+2 and −2-2 (product = 4), while in NaClNaCl, the charges are +1+1 and −1-1 (product = 1). Since the charges in MgOMgO are higher, the electrostatic attraction is stronger, leading to a higher lattice enthalpy.

Ionic or Electrovalent Bond - Revision Notes & Key Formulas | CBSE Class 11 Chemistry