Suggest reasons why the following do not exist as stable molecules: (a) H3 ; (b) HHe ; (c) He2;

Suggest reasons why the following do not exist as stable...

Key Concepts

Electronic Structure and Electron Counting

The stability of a molecule depends critically on its electronic structure, including proper electron count and pairing. Molecules with an odd number of electrons or those that cannot achieve closed-shell configurations tend to be unstable, as they lack sufficient bonding interactions to offset repulsions. This concept is crucial when considering species like neutral H3, where the electron count does not favor a stable bonding arrangement.

Orbital Overlap and Covalent Bonding

For a stable covalent bond to form, atomic orbitals must overlap effectively to create a bonding molecular orbital. In cases such as H3 and compounds involving helium (like HHe and He2), the spatial distribution and energy levels of the orbitals do not align well to produce significant overlap, which results in insufficient bonding energy to support a stable molecule.

Noble Gas Inertness

Noble gases, such as helium, have completely filled valence electron shells, rendering them chemically inert under typical conditions. This concept explains why species like HHe and He2 are not stable, as helium’s reluctance to participate in bonding interactions, due to its high ionization energy and lack of available orbitals for bonding, prevents the formation of stable compounds.

Charge Distribution and Formal Charge Considerations

The distribution of electrons and the resulting formal charges within a molecule affect its stability. Molecules like H3O, when considered as a neutral species, suffer from improper charge distribution that destabilizes the structure. Unlike the hydronium ion H3O?, where the positive charge helps stabilize the configuration, a neutral H3O would not have a favorable arrangement of electrons, leading to its instability.

Transcript

00:01 Right, so we're given four different sets of supposed compounds, and we're going to try to figure out why they cannot form a lot structure.

00:08 So why can this configuration not happen, right, stable molecules? so if you look at h3, so each hydrogen has one valence electron, right? and normally what hydrogen is going to do is hydrogen is a 1s, right? and each hydrogen looks like this.

00:28 To be stable, it either needs to get rid of this electron, and most likely with another non -matter what it's going to do, is it needs to share this other electron, right? or if you want to look at a non -electron configuration format, you can't, it only needs to have two electrons around it to be stable because the novogasas want to look like the i'm going to raise it.

01:08 So we're given four different sets of compounds or compounds that are not stable, and we're going to figure out why.

01:17 And the good way is just to draw the looze that structure if it's possible.

01:21 Most of them can't be possible, right? but we're going to go with the lois dot structures to see.

01:26 So hydrogen, each hydrogen has one valence electron, right? so hydrogen, we know the hydrogen stable with two electrons, right? so each of them has one, so it shares one, right? and that's it.

01:40 This hydrogen is stable, this hydrogen is stable, and this hydrogen is not stable.

01:44 You cannot form a triangle.

01:46 There's absolutely no way to do it.

01:47 I can't bond.

01:49 This is not going to find a cyclic hydrogen.

01:51 That's not possible.

01:52 First of all, where are you going to put that extra electron, right? the idea of sharing it is so it looks like it closes noble gas.

01:58 You can think about it that way, right? and the reason hydrogen only needs two electrons is because the closest noble gas to it is helium.

02:05 My helium is stable with two electrons right if you look at hydrogen hydrogen hinder looks like this right and i have another hydrogen here and let's draw near each other so i have one hydrogen here right and if i also bring another hydrogen and then to share its electrons it will look like this where you're gonna put the extra other electron you can't have there's no space for a third hydrogen around it so this cannot be formed because only two of those electrons will pair and then you would have a hydrogen radical just floating around, and that's just not possible.

02:39 So we have hydrogen and helium.

02:41 So hydrogen looks like this, and then helium has two valance electrons.

02:46 Now, the issue here is that helium is already stable.

02:50 Hydrogen is not, but helium is already stable.

02:52 And even if you were to bring another hydrogen, then you destabilize the helium...

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