Because hydrogen is located somewhat centrally in an electronegative sense, it is necessary for the counterion to be exceptionally electropositive for the hydride to possibly be accurately described as truly behaving ionic.
The results consist of metallic matrices with dissolved, often stoichiometric or near so, concentrations of hydrogen, ranging from negligible to substantial.
Due to the total number of possible binary saturated compounds with carbon of the type CnH2n+2 being very large, there are many group 14 hydrides.
Going down the group the number of binary silicon compounds (silanes) is small (straight or branched but rarely cyclic) for example disilane and trisilane.
Non-classical hydrides are those in which extra hydrogen molecules are coordinated as a ligand on the central atoms.
[6] The isolation of monomeric molecular hydrides usually require extremely mild conditions, which are partial pressure and cryogenic temperature.
Relativistic effects play an important role in determining the energy levels of molecular orbitals formed by the heavier elements.
For example, based on its position in the 12th column of the periodic table alone, mercury(II) hydride would be expected to be rather deficient.
The table below shows the monomeric hydride for each element that is closest to, but not surpassing its heuristic valence.
In the case of chromium, for example, stearic hindrance ensures that both the octahedral and trigonal prismatic molecular geometries for CrH6 are thermodynamically unstable to rearranging to a Kubas complex structural isomer.
Where available, both the enthalpy of formation for each monomer and the enthalpy of formation for the hydride in its standard state is shown (in brackets) to give a rough indication of which monomers tend to undergo aggregation to lower enthalpic states.
This means that it is energetically favourable for a mole of monomeric LiH to aggregate into the ionic solid, losing 230 kJ as a consequence.
For some elements, when hydrogen content exceeds its solubility, the excess precipitates out as a stoichiometric compound.