Im not sure if this question belongs here or in another community. I was wondering if the direction that we apply a force in order to break a bond matters and how it affects strength. Say we have one compound e.g NaCl. Compared to breaking the bond between the Na ion and Cl ion in a tensile manner, would it require a different force to "tear" it in a shearing manner.
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Why, surely the tensile strength and shear strength are two different things, otherwise why would we bother to have two different terms for those? – Ivan Neretin Apr 04 '20 at 01:31
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Normally those two types of forces are mentioned for materials in bulk and they make sense in that context. I was wondering if the differences still applied down to the atomic level so I made sure to specify that I am talking about "one compound" in the question. – A.AK Apr 04 '20 at 02:53
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2I think the problem is not that trivial. You are talking about cleavage anisotropy of crystals. Search this keyword. NaCl crystal is isotropic, it implies directions does not matter. – AChem Apr 04 '20 at 03:36
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2Although you ask specifically about NaCl, unfolding proteins using force (breaking H bonds) the direction in which the force is applied does matter as does the rapidity of applying that force. – porphyrin Apr 04 '20 at 06:55
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Twenty kilograms of NaCl is still one compound. You probably wanted to say "one molecule" or "one formula unit". – Ivan Neretin Apr 04 '20 at 09:03
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@M.Farooq Thank you, I will look more into it but from an initial glance it seems like that the papers looking into that topic are still talking about crystal structures in bulk – A.AK Apr 04 '20 at 13:54
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@porphyrin thats very interesting. That definitely says something about directionality affecting strength at a molecular level. I will look more into it. Thanks – A.AK Apr 04 '20 at 13:56
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@IvanNeretin Yea it felt weird typing "compound" but I didn't want to say molecule because NaCl is not covalently bonded. – A.AK Apr 04 '20 at 13:58
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1There is an example here 'Pulling geometry defines the mechanical resistance of a beta-sheet protein', Brockwell, et al.. Nature Structural Biology (2003), 10, 731 – porphyrin Apr 05 '20 at 07:30
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Thank you for the reference. In the example they present, it seems to have required a lesser force to shear than to rupture. The article is examining somewhat of a "bulk" material with multiple hydrogen bonds but the results are still interesting. – A.AK Apr 05 '20 at 19:51
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A possible real-world example of directional force use may be apparent from the commercial application of so-called magnetizers (see discussion here).
I once experimented with a small inexpensive one and it appears to accelerate select reactions.
A commercial example for reducing the amount of chlorinating agent required in public swimming pools in England demonstrated success to reduce scale build-up, moderate pH and increase available chlorine in a pool, employing magnetic field treatments here.
Some discussion details on how magnetic fields may potentially impact chemical reactions per comments posted previously on StackExchange.
An important point concerns radical based reactions, which per chlorine-based chemistry in sunlight treated swimming pools, is likely extensive and may be potentially impacted. This could particularly alter pool chemistry especially surrounding the fate of the chlorine radical, where an alteration of spins along with a possible decrease in the reverse recombination reaction to Cl2 via the normal reactions:
$\ce{Cl2 + hv -> •Cl + •Cl}$
$\ce{ •Cl + •Cl -> Cl2}$
where the above reaction is impaired due to spin changes by magnetic fields, resulting in more chlorine radicals. The latter can slowly react with water, for example, importantly producing the powerful hydroxyl radical:
$\ce{•Cl + H2O <=> HCl + •OH}$
Source: See Table l in "Photochemistry of HCl and Other Minor Constituents in the Atmosphere of Venus" by Prinn, R.G. as an example.
More detail on mechanics is provided by this source, to quote:
Radical pairs in chemical reactions are known to respond to magnetic fields. This involves pairs of transient radicals being created simultaneously, such that the two electron spins, one on each radical, are correlated. Their chemical fate is largely dictated by weak magnetic interactions, so that you get radicals with unpaired electron spins either antiparallel (singlet state) or parallel (a triplet state).
Even though the interactions of electron spins with an applied field is very weak, there is enough time to affect the balance between singlet and triplet radical pair states and therefore to change the yields of the products formed from them,...
