When does an ionic bond form?

An ionic bond is formed between two atoms when there is a significant electronegativity difference i.e. (ΔEN > 1.7).

Ionic bonds have the identification of being formed when there is a great electronegativity difference between the constituent atoms. One of the constituent atoms has to behave like an anion and the other as a cation to make the bond, ‘Ionic’.

In a bond, two electrons are surely placed together which we show by drawing a line but electrons of constituent atoms never leave the vicinity of atoms. This makes the assumption, “electrons leave or get added into atoms to make bonds” quite wrong. Actually, it is the ‘vicinity sharing’ of atoms where electrons spin near one another, and we call it a bond.

An ionic bond is very similar to a covalent bond except for the charges expressed over atoms because an ionic bond contains cation-anion bond linkage whereas a covalent bond has two atoms mutually sharing electrons to make a bond i.e. completing their octets to get stable.

In short, an ionic bond is actually a covalent bond, with a high polarity among constituent atoms.

Here is a table that differentiates the ionic bond from covalent (polar and nonpolar) bonds.

Type of bond Polarity Electronegativity difference (ΔEN)
Ionic bond Polar above 1.7
Covalent bond Polar 0.4 to 1.7
Nonpolar 0 to 0.40

Electronegativity and electropositivity

The ability of an atom to attract a shared pair of electrons is termed electronegativity. The electropositivity is exactly the inverse of electronegativity. It is the ability of an atom to donate or lose the shared electronic pair. Electronegative atoms tend to be anions whereas electropositive ones become cations.

Here are some examples which have an electronegativity difference, more than (1.7), so these are perfectly ionic compounds.

  • NaCl

The electronegativity of sodium (Na) is 0.93 and chlorine (Cl) is 3.16. The electronegativity difference among these atoms is 2.23 which is more than 1.7(least limit to be ionic). So, NaCl is perfectly an ionic compound.

When does an ionic bond form?

Similarly,

  • Sodium sulphite (Na2SO3)
  • Sodium hydrogen phosphate (NaHPO4)
  • Magnesium sulphate (MgSO4)
  • Potassium phosphate (K3PO4)
  • Potassium iodide (KI)
  • Sodium hydroxide (NaOH)
  • Sodium carbonate (Na2CO3)
  • Sodium bicarbonate (NaHCO3)
  • Sodium fluoride (NaF)

These are some examples of ionic compounds.

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