Properties
HHe+ cannot be prepared in a condensed phase, as it would protonate any anion, molecule or atom with which it were associated. However it is possible to estimate a hypothetical aqueous acidity using Hess's law:
| HHe+(g) | → | H+(g) | + He(g) | +178 kJ/mol | |
| HHe+(aq) | → | HHe+(g) | +973 kJ/mol | ||
| H+(g) | → | H+(aq) | – 1530 kJ/mol | ||
| He(g) | → | He(aq) | +19 kJ/mol | ||
| HHe+(aq) | → | H+(aq) | + He(aq) | – 360 kJ/mol |
A free energy change of dissociation of –360 kJ/mol is equivalent to a pKa of –63.
The length of the covalent bond in HeH+ is 0.772 Å.
Other helium hydride ions are known or have been studied theoretically. HeH+
2, which has been observed using microwave spectroscopy, has a calculated binding energy of 6 kcal/mol, while HeH+
3 has a calculated binding energy of 0.1 kcal/mol.
Read more about this topic: Helium Hydride Ion
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