Ionic or Electrovalent Bond

An ionic bond is a type of chemical bond formed through the transfer of electrons from one atom to another. It typically occurs between a metal and a nonmetal.

• In this process, the metal atom loses one or more electrons to become a positively charged ion (cation), while the nonmetal gains these electrons to become a negatively charged ion (anion).
• The electrostatic force of attraction between the oppositely charged ions holds them together in a stable structure, forming an ionic bond.
• Ionic bonds are responsible for the formation of ionic compounds, such as sodium chloride (NaCl).
• These compounds exhibit unique properties, including high melting and boiling points, solubility in water, and the ability to conduct electricity in molten or aqueous states.
• The ionic bond allows atoms to achieve a stable electron configuration, often following the octet rule, which makes them energetically stable.

(a) Formation of Ionic Bond in NaCl (Sodium Chloride):

1. Sodium (Na): Atomic number 11, configuration 2,8,1. It has 1 valence electron in its outermost shell (M shell).
2. Chlorine (Cl): Atomic number 17, configuration 2,8,7. It has 7 valence electrons and needs 1 more electron to complete its octet.
3. Sodium loses 1 electron, becoming a Na⁺ cation (positively charged ion). New configuration of Na⁺: 2,8 (stable octet).
4. Chlorine gains the electron lost by sodium, becoming a Cl⁻ anion (negatively charged ion). New configuration of Cl⁻: 2, 8, 8 (stable octet).
5. The oppositely charged ions (Na⁺ and Cl⁻) are held together by the electrostatic force of attraction, forming an ionic bond.
6. The compound formed is sodium chloride (NaCl).

$$\text{Na⁺ + Cl⁻ → NaCl}$$

Formation of Ionic bond of NaCl 

(b) Formation of Ionic Bond in MgCl₂ (Magnesium Chloride):

1. Magnesium (Mg): Atomic number = 12, electronic configuration = 2, 8, 2.
2. Magnesium has 2 valence electrons in its outermost shell. It needs to lose 2 electrons to achieve a stable octet configuration.
3. Chlorine (Cl): Atomic number = 17, electronic configuration = 2, 8, 7.
4. Chlorine has 7 valence electrons in its outermost shell. Each chlorine atom needs 1 electron to complete its octet.
5. Magnesium loses 2 electrons, forming a Mg²⁺ cation with a stable configuration of 2, 8.
6. Each chlorine atom gains 1 electron from magnesium to form a Cl⁻ anion with a stable configuration of 2, 8, 8.

Mg → Mg²⁺ + 2e⁻

Cl + e⁻ → Cl⁻

Magnesium loses 2 electrons, and these are gained by 2 chlorine atoms.

Mg²⁺ + 2Cl⁻ → MgCl₂

Formation of Ionic bond in MgCl₂ molecule

(c) Formation of Ionic Bond in KF (Potassium Fluoride):

1. Potassium (K): Atomic number = 19, electronic configuration = 2, 8, 8, 1.
2. Potassium has 1 valence electron in its outermost shell. And it needs to lose 1 electron to achieve a stable octet configuration.
3. Fluorine (F): Atomic number = 9, electronic configuration = 2, 7.
4. Fluorine has 7 valence electrons in its outermost shell. And it needs to gain 1 electron to complete its octet.
5. Potassium loses 1 electron, forming a K⁺ cation with a stable configuration of 2, 8, 8.
6. Fluorine gains 1 electron from potassium to form a F⁻ anion with a stable configuration of 2, 8.

K → K⁺ + e⁻

F + e⁻ → F⁻

Potassium loses 1 electron, and fluorine gains 1 electron, ensuring charge balance:

K⁺ + F⁻ → KF

Formation of Ionic bond in KF molecule

(d) Formation of Ionic Bond in CaO (Calcium Oxide):

1. Calcium (Ca): Atomic number = 20, electronic configuration = 2, 8, 8, 2.
2. Calcium has 2 valence electrons in its outermost shell. And it needs to lose 2 electrons to achieve a stable octet configuration.
3. Oxygen (O): Atomic number = 8, electronic configuration = 2, 6.
4. Oxygen has 6 valence electrons in its outermost shell. And it needs to gain 2 electrons to complete its octet.
5. Calcium loses 2 electrons, forming a Ca²⁺ cation with a stable configuration of 2, 8, 8.
6. Oxygen gains 2 electrons from calcium to form an O²⁻ anion with a stable configuration of 2, 8.

Ca → Ca²⁺ + 2e⁻

O + 2e⁻ → O²⁻

Calcium loses 2 electrons, and oxygen gains 2 electrons, ensuring charge balance:

$$\text{Ca²⁺ + O²⁻ → CaO}$$

Formation of Ionic bond in CaO molecule

Melting point and boiling point of some ionic compounds:

1. Ionic compounds are solid and hard due to the strong electrostatic force between positive and negative ions but are generally brittle, breaking when pressure is applied.
2. They have high melting and boiling points because a large amount of energy is needed to overcome the strong ionic bonds.
3. Ionic compounds are typically soluble in water, as water's polarity helps separate the ions, but they are insoluble in non-polar solvents like kerosene or petrol.
4. In solid form, ionic compounds do not conduct electricity because the ions are fixed in place in the crystal lattice and cannot move.
5. In molten form or aqueous solutions, ionic compounds conduct electricity as the ions are free to move and carry electric charge.
6. Ionic compounds are characterised by a rigid lattice structure, which provides stability but limits flexibility.

An ion is a charged particle which is formed due to the gain or the loss of one or more electrons by an atom.

A metallic atom, which loses electron(s), becomes a positively charged ion and is known as a cation.

A non-metallic atom, which gains electron(s), becomes a negatively charged ion and is known as an anion.

A metallic element, whose one atom readily loses electron(s) to form a positively charged ion, is an electropositive element.

A non-metallic element, whose atom readily accepts electron(s) to form a negatively charged ion, is an electronegative element.

The cation and the anion being oppositely charged attract each other and form a chemical bond. Since this chemical bond formation is due to the electrostatic force of attraction between a cation and an anion, it is called an electrovalent (or an ionic) bond.

The chemical compounds formed as a result of the transfer of electrons from one atom of an element to one atom of another element are called ionic (or electrovalent) compounds.

The number of electrons that an atom of an element loses or gains to form a electrovalent bond is called its electrovalency.

An ionic bond is formed by the complete transfer of one or more electrons from an electropositive atom to an electronegative atom, resulting in oppositely charged ions that attract each other.

Key conditions for ionic bond formation:

• One atom must have low ionisation enthalpy (easily loses electron) — typically a metal

• The other must have high electron affinity (easily gains electron) — typically a non-metal

• Large difference in electronegativity between the two atoms

Example: Na + Cl → Na⁺ + Cl⁻ → NaCl

• Sodium (2,8,1) loses 1 electron → Na⁺ (2,8)

• Chlorine (2,8,7) gains 1 electron → Cl⁻ (2,8,8)

Ionic solids are crystalline structures containing cations and anions held together by strong electrostatic ionic bonds.