Applications of Particle in a Box model (Chemistry)

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Reply 20

EierVonSatan

Lifeisnice

What physical reality does n=2 represent

By itself? Nothing

and what does it mean when compared against n=3?

Energy of the particle is greater when n = 3 compared to n = 2, the probability of finding a particle at any one place is altered.

Reply 21

Kyle_S-C

Lifeisnice

What physical reality does n=2 represent, and what does it mean when compared against n=3?

This image shows the states corresponding to n=1, 2, 3 and 4 for butadiene. As you can see, each state can be occupied by 2 electrons and there's 1 pi electron per carbon (so 4 in total).

Filling up from the bottom, since fewer nodes means lower energy (generally), you have the n=1 and n=2 states filled and the others unfilled. This means that the overall picture looks a bit like there's a big partial pi-bond across the whole molecule and then a set of two partial pi-bonds between the outer pairs of atoms (i.e. 1 with 2 and 3 with 4).