Re: [Phys-l] chemical bonds

[chuck britton <cvbritton@mac.com>]

Hear, hear ! ! !

The amount of confusion/erroneous words etc. surrounding this 'bond' 
thing is amazing.
The Bio/Nutrition/Health crowd is especially susceptible but we all 
share some guilt.


At 6:44 PM -0700 12/15/10, John Denker wrote:
> <snip>
> ==========================
>
> The other weird thing about bonds is that chemists more-or-less universally
> speak in terms of the bond energy (or "heat of formation") as a positive
> number, even though it makes a negative contribution to the energy content
> of the sample.  Let's be clear:  A stronger bond means a more-negative (or
> less-positive) energy content.  This leads to confusion because in almost
> any other context people would talk about the _energy content_ directly (for
> instance, as we saw in connection with the Bernoulli equation).


Nuclear Physics keeps this unClear by also referring to positive 
nuclear bond energies.
I tried to clear this up by having the kids calculate the 'Mass per 
Nucleon' for a selection of nuclei at each end and the middle of the 
atomic chart. We plotted the results and see a 'roller coaster' with 
each end being positive and a broad dip in the middle (around 57Fe).

Nuclear reactions 'roll' down hill releasing their excess mass as energy.

This seems easier to internalize than keeping track of positive bond 
energies etc.



How often do we hear that living things get their energy from 
'breaking the ATP bonds'?
	shudder!!