which is more stable Hydronium or hydride ion

[Bernoull]

I've read the hydride ion is very unstable and I was curious if it's less stable than a proton, if so, why?

It's clear that both ions have charges of equal magnitude therefore charge density should be the same - except if one of the ion's is smaller. My theory is that the effective nuclear charge of the hydride is greater than the proton since the former has 2 electrons and consequently the electrons are pulled closer towards the nucleus thus reducing atomic radius. This results in higher charge density which should imply less stability for the hydride.

Im not sure if this is the reason or if something else explains hydride's greater instability compared to proton (assuming this is true in the first place).

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[bjb305]

I've read the hydride ion is very unstable and I was curious if it's less stable than a proton, if so, why?

It's clear that both ions have charges of equal magnitude therefore charge density should be the same - except if one of the ion's is smaller. My theory is that the effective nuclear charge of the hydride is greater than the proton since the former has 2 electrons and consequently the electrons are pulled closer towards the nucleus thus reducing atomic radius. This results in higher charge density which should imply less stability for the hydride.

Im not sure if this is the reason or if something else explains hydride's greater instability compared to proton (assuming this is true in the first place).

the hydride ion does not have a higher effective nuclear charge. The effective nuclear charge is measured based on the number of protons in the nucleus and the number of core electrons. Essentially in both cases, they each have 1 proton and zero core electrons (outer shell electrons don't count) giving them the same effective nuclear charge. However, in the case of the hydride ion, that ONE proton now has to exert it's force over two electrons and has less pull. This makes the hydride less stable. It's kind of like the same reasoning behind why you never see Na with a negative charge and never see Cl with a positive charge

 

[Ibn Rushd]

Just to clarify, a proton is not the same thing as a hydronium ion. They're used interchangeably in acid/base chem, but as far as their structures and properties are concerned, they differ.

 

[Bernoull]

Thanks for the responses:

Ibn Rushd Just to clarify, a proton is not the same thing as a hydronium ion. They're used interchangeably in acid/base chem, but as far as their structures and properties are concerned, they differ.

Ibn Rushd thanks for the input, I was using the term "proton" loosely. I know proton is the entity in the nucleus with neutrons and hydronium ion is a "hydrated proton-H3O+". Specifically, what I have in mind is an "ionised Hydrogen atom H+"


bjb305: Many thanks for the explanation, unfortunately I didn't quite follow your reasoning.

bjb305: the hydride ion does not have a higher effective nuclear charge. The effective nuclear charge is measured based on the number of protons in the nucleus and the number of core electrons. Essentially in both cases, they each have 1 proton and zero core electrons (outer shell electrons don't count) giving them the same effective nuclear charge.

Firstly, the Zeff (effective nuclear charge) is simply a measure of the "experienced electrostatic force" between a given electron and the nuclear proton(s). For neutral H, it's essentially Coulomb's force since there's 1 proton and a single 1s electron. However, for atoms with more than 1 electron, the Zeff accounts for repulsion (Shielding) that happens b/t electrons within and across electronic shells which lessens Coulomb's force. Zeff = Z (nuclear charge) - S (shielding constant). See
http://www.carlalbert.edu/nmaxwell/Chemistry/pdf/ch 7 new.pdf

Given this, I don't see how both H+ and H- can have the same Zeff. The positive nuclear charge is the same, but H+ has lost its e and H- has 2e.

bjb305: However, in the case of the hydride ion, that ONE proton now has to exert it's force over two electrons and has less pull.This makes the hydride less stable.It's kind of like the same reasoning behind why you never see Na with a negative charge and never see Cl with a positive charge

From a Coulomb force perspective, H- should have a greater electrostatic force notwithstanding the shielding effect and the single proton.
F=kqQ/r^2. It also occured to me that H+ has no Zeff since it's electronless!! F=zeroN. Thanks for your help though.