Cohesion is the tendency for the same type of molecules to stick together due to intermolecular forces. Water molecules are cohesive because of their polarity and ability to form hydrogen bonds. An oxygen atom with a partial negative charge in one water molecule can bind to a hydrogen atom with a partial positive charge in another water molecule, forming a hydrogen bond. Each water molecule can form up to four hydrogen bonds with other water molecules. Molecules of water will group together to form droplets. The molecules at the surface are exposed to air but are more attracted to themselves than to the molecules in the air. The stronger attraction to other water molecules because of the hydrogen bonds creates a pull inwards, which generates surface tension. Due to this phenomenon, the surface of the water can resist rupture. Because of this, small objects appear to float, and small insects can walk on water as long as they don't break the cohesive forces on the surface.