INO-16

HSAB hardness snapshot

η = (I − A)/2. Absolute chemical hardness.

Reading speed

AcidityPearson HSAB

Governing equation

\eta=\tfrac12(I-A)

where

I: Ionisation energy (eV)
A: Electron affinity (eV)
\eta: Hardness (eV)
\chi: Mulliken EN (eV)

Lecture brief

Historical brief

Pauling and Allred–Rochow electronegativity, Kapustinskii lattice energy, CFSE and Goldschmidt radii organise the periodic solid. The sheets predict bond character and crystal packing. This sheet (INO-16 — HSAB hardness snapshot) is the form associated with Pearson HSAB. Working symbols: $I$ , $A$ $\rightarrow$ $\eta$ , $\chi$ . Pearson: hard acids bind hard bases. Parr identified η with the HOMO–LUMO gap / 2.

Purpose

Purpose: compute

\eta

\chi

from

I

A

in Inorganic chemistry via

\eta=\tfrac12(I-A)

η = (I − A)/2. Absolute chemical hardness. Use it when a real inorganic chemistry question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

I = 13.600\,\mathrm{eV}

A = 0.800\,\mathrm{eV}

, the governing relation

\eta=\tfrac12(I-A)

yields

\eta = 6.400\,\mathrm{eV}

\chi = 7.200\,\mathrm{eV}

. I and A in eV (gas-phase or Koopmans snapshot). Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Ionisation energy I13.6 eVElectron affinity A0.8 eV

Outputs

Hardness \eta6.400 eV
Mulliken EN \chi7.200 eV

Reading speed

Watch on YouTube

Free library

Full library

Free PDF / open book

YouTube channels

00:0 / 00:08

Narration of this film

I and A in eV (gas-phase or Koopmans snapshot).

Pearson: hard acids bind hard bases. Parr identified η with the HOMO–LUMO gap / 2.

Reading speed

Watch on YouTube