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Inshort Surface tension occurs due to imbalance of the intermolecular forces of attraction on water molecules. At the surface it is more so net force is inwards.

I read somewhere on this app that "which liquid has zero surface tension". But is it possible to have zero surface tension, because surface tension occurs if there is surface but if surface tension is zero it means there is no surface. Which doesn't make sense.

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  • $\begingroup$ @JohnRennie no, I saw that question and I had a doubt how surface tension can be zero $\endgroup$ Jan 11, 2020 at 20:18

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This happens at the critical point, where the line between liquid and gas in a phase diagram terminates. There are then self-similar density fluctuations at all length scales, which leads to critical opalescence. The surface becomes infinitely large, or one could indeed also say that there is no surface anymore.

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Surface tension is ultimately a property of liquids that stems from their cohesion, or the attractive forces between molecules of that liquid. Take water, for instance. A partially positive hydrogen atom in one molecule of water may temporarily bond to a partially negative oxygen atom in another, leading to a substantial cohesive force. Cohesion and surface tension may also result from the effects of dipole-dipole attraction in polar molecules, as in ammonia, although to a slightly smaller degree.

On the other hand, nonpolar molecules which don’t experience the effects of hydrogen bonding, like liquid nitrogen, are generally not attracted to one another except via London dispersion forces, which result in weak cohesion and, thus, weak, but nonzero, surface tension. Because of these London dispersion forces, all liquids have surface tension to some degree at normal pressures.

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