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How do hydrogen bonds form between molecules?
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molecule
Several methods of representing a molecule's structure. In Lewis structures, element symbols represent atoms, and dots represent electrons surrounding them. A pair of shared electrons (covalent bond) may also be shown as a single dash. The ball-and-stick model better illustrates the spatial arrangement of the atoms. For aromatic compounds, the Kekulé structure is common, in which each bond is represented by a dash, carbon atoms are implied where two or more lines meet, and hydrogen atoms are usually omitted. Bond-line formulas, similar to the Kekulé structure, are often used for complex nonaromatic organic compounds. Sugars are often drawn as Fischer projections, in which the carbon “backbone” is drawn as a straight vertical line, with carbon atoms implied where horizontal lines intersect the vertical one.
A hydrogen bond forms through an electrostatic attraction between a hydrogen atom that is covalently bonded to a highly electronegative atom (such as fluorine, nitrogen, or oxygen) and another electronegative atom that possesses an unshared pair of electrons.12
The process occurs as follows:
- Polarization: Because the donor atom (F, N, or O) has a high affinity for electrons, it shares electrons unequally with the hydrogen atom. This causes the hydrogen to acquire a slight positive charge, while the donor atom takes on a slight negative charge.13
- Electrostatic Attraction: The hydrogen atom, now slightly positive, is attracted to the unshared electron pair of a nearby electronegative atom (the acceptor), which carries a slight negative charge.12
- Alignment: The hydrogen atom typically lies on a straight line between the nuclei of the donor and acceptor atoms.4
While weaker than ionic or covalent bonds, hydrogen bonds are stronger than van der Waals forces. They are essential in determining the structure of biological molecules like proteins and DNA, and they significantly influence the physical properties of substances like water.154