Understanding the concept of surface tension.

Oct 2017
Isn't those molecules that are at curved surfaces gonna feel a downward intermolecular force due to molecule below it, and it should cancel the upward attraction caused by the molecule above it.
No, it's an upward molecular force, which balances the weight of the pin.

Maybe this picture will help:


Source: Surface tension - Wikipedia

Notice the directions on the arrows... the van der Waal's forces act to make the water "stickier", not "slippier".
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Jun 2016
There are attractive intermolecular forces and repulsive intermolecular forces
they balance each other at a particular intermolecular distance (dependent of temperature)

In the picture you can see that the cohesion of the paperclip is deforming the surface.
If you work out the balance of intermolecular forces acting along that curve,
you will find that they match the weight of the paper clip.

As long as the forces due to the weight of the clip do not exceed the forces holding the molecules together
the whole system will reach a balance, with the clip being supported on top of the water.