The degree to which a bond behaves as ionic, estimated from the dipole moment or electronegativity difference.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
Percent ionic character describes how close a bond is to the fully ionic model, expressed as a percentage. It can be estimated by comparing the measured dipole moment with the dipole moment expected if one full electron charge were transferred across the bond length, so percent ionic equals measured dipole divided by that ideal value, times 100. No bond is completely ionic, since even CsF retains some covalent character. As a rough guide, bonds with an electronegativity difference above about 1.7 are considered mostly ionic. The concept shows that bonding lies on a continuum.
Key ideas: Two estimation methods: from dipole moment as measured divided by e times r, and from Pauling's formula 1 minus exp of minus (delta chi squared divided by 4), where delta chi is the electronegativity difference. For delta chi equal to 1.7 this gives about 50 percent ionic. HF is about 41 percent and NaCl in gas phase about 80 percent.
Common mistakes and connections: Students treat 100 percent ionic as achievable, but the best examples such as CsF are near 90 percent at most. Also, a threshold such as 1.7 is only a rough guide, and many compounds with a smaller difference, like AlCl3 or HF, behave unusually. Connects to bond polarity, dipole moment, Fajans' rules and electronegativity.
Hannay-Smyth estimate: ionic character rises smoothly with electronegativity difference and passes about 50 percent near a difference of 1.7. The interactive lesson shows this as a live animation or chart.
HCl has a measured dipole moment of about 1.08 D and is about 17 percent ionic.
The degree to which a bond behaves as ionic, estimated from the dipole moment or electronegativity difference.
Percent Ionic Character is a intermediate topic in Bonding & Molecular Structure. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Bonding & Molecular Structure first: Bond Polarity, Dipole Moment, Polar and Nonpolar Molecules.
The next topics in Bonding & Molecular Structure are Fajans' Rules and Polarizability.
Yes. The interactive lesson includes a self-check question on Percent Ionic Character, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Percent Ionic Character is topic 24 of 104 in Bonding & Molecular Structure.