In still other cases, the crystallographer may detect that the covalent structure deduced for the molecule was incorrect, or changed.
2.
What is in most respects a purely covalent structure can support metallic delocalization of electrons; metallic carbon nanotubes are one example.
3.
Because nucleic acids are normally linear ( unbranched ) polymers, specifying the sequence is equivalent to defining the covalent structure of the entire molecule.
4.
Diamondoid structures and other stiff covalent structures, if achieved, would have a wide range of possible applications, going far beyond current MEMS technology.
5.
In 1992, Drexler published " Nanosystems : Molecular Machinery, Manufacturing, and Computation ", a detailed proposal for synthesizing stiff covalent structures using a table-top factory.
6.
For example, in the hydrogen molecule, classic valence bond theory uses two 1s atomic orbitals ( a and b ) on the two hydrogen atoms respectively and then constructs a covalent structure :-
7.
So I assume that the " intra " molecular case you refer to would just be an " intermolecular " bond between two atoms that happen to be far apart in the basic covalent structure of the same molecule ( contributing, e . g . to protein folding ).
8.
Thus, rather than having the diamond-cubic covalent structure, lead forms metallic bonds, in which only the p-electrons are delocalized and shared between the Pb 2 + ions, resulting in a face-centered cubic structure like those of the similarly-sized divalent calcium and strontium.
9.
In contrast, ?-tin ( nonmetallic form, or gray tin ), which is stable below, is brittle . ?-tin has a diamond cubic crystal structure, similar to diamond, silicon or germanium . ?-tin has no metallic properties at all because its atoms form a covalent structure in which electrons cannot move freely.
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