Energy Level Diagrams Confusion

[HarveyD]

Why do some diagrams have the excited state/ionization level using a negative eV value and increasing up to 0? :S

Edit: Wait, think i got it
Positive eV = Emit
Negative eV = Absorb?

[xZero]

no special reason, it just wants to use the max excited state as a 0 point, its completely arbitrary.

[HarveyD]

ah k, just overthinking it

thanks

[Lasercookie]

It would be comparing it to the energy below the ionisation level, where ionisation energy level is 0.
So if that is 0, then the energy level between ionisation level and a state would be negative.

If the graph refers to energy above the ground state (where the ground state level is 0) then you would get positive values for the other states.

I know what you're talking about, but I just can't find an example picture of one at the moment. Can you post a picture of what you're talking about? The past few VCAA's have referred to energy above the ground state.

Edit: As xZero said, arbitrary values.

[HarveyD]

if you have heinemann, was just looking at the diagrams given for qs 3 and 8 of 12.2

[mark_alec]

It is conventional to denote bound states by negative energy, while free states have a positive energy.