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 alkyl 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 was formed when the particles was coated with dodecane chains while coating with short alkane chains (butane, octane and decane) resulted in inhomogeneous, porous films. The difference in monolayer structure could be related to the interparticle forces and it was concluded that the formation of ordered colloidal monolayer required that the interparticle attraction is sufficiently weak allowing the formation of ordered domains which can deform during drying.