A new concept of the formation of the monolayer of colloidal particles on the air-liquid interface based on a new simple model to consider the relation between the interparticle forces and the monolayer structures was proposed. Colloidal monolayers were formed by spreading monodisperse silica particles coated with alkoxyl chains of different length at the air-benzene interface and picking up the floating clusters or ordered domains with a mica substrate. Polycrystalline, two-dimensional monolayers were formed when the particles were coated with dodecyl chains, while coating with short alkoxyl chains (butyl and decyl chains) resulted in inhomogeneous, porous films. The difference in monolayer structure could be related to the interparticle forces at the air-liquid interface which can be controlled by changing the degree of immersion or the range of the repulsive interaction. It was concluded that the formation of an ordered colloidal monolayer required that the interparticle attraction is sufficiently weak allowing the formation of ordered domains which can deform during drying.