S2.4.2 Position in the bonding triangle Notes

Electronegativity and Bond Character: Understanding the Bonding Triangle

The Three Corners of the Bonding Triangle

The triangle's corners represent the "pure" forms of bonding:

1. Ionic bonding: Complete transfer of electrons (e.g., NaCl).
2. Covalent bonding: Sharing of electrons (e.g., H₂).
3. Metallic bonding: Delocalized electrons shared across a lattice of metal cations (e.g., Cu).

Intermediate Bond Types

The triangle's sides represent bonds with mixed characteristics:

1. Ionic-covalent: Polar covalent bonds with partial ionic character.
2. Covalent-metallic: Bonds in metalloids or semiconductors.
3. Ionic-metallic: Bonds in alloys or compounds with both metallic and non-metallic elements.

Parameters for Classification

The position of a compound in the bonding triangle is determined by two key parameters:

1. Electronegativity difference (Δχ): Indicates the ionic-covalent character. A larger Δχ suggests greater ionic character.
2. Mean electronegativity (χ̄): Indicates the metallic-covalent character. A higher χ̄ suggests more covalent character.

Determining a Compound's Position in the Bonding Triangle

To locate a bond in the bonding triangle:

1. Calculate $Δχ$: Subtract the smaller electronegativity from the larger one.
   $$
   \Delta\chi = \chi_{\text{higher}} - \chi_{\text{lower}}
   $$
2. Calculate $\bar{\chi}$: Take the average of the electronegativities.
   $$
   \bar{\chi} = \frac{\chi_{\text{higher}} + \chi_{\text{lower}}}{2}
   $$

Bond Character and Material Properties

The bonding triangle provides insights into the physical and chemical properties of compounds, such as melting point, solubility, and electrical conductivity.

Ionic Compounds

1. Example: Sodium chloride (NaCl)
2. Bond Character: Predominantly ionic.