The scattering of light by the molecules/particles present in the air (size is generally 1/10th of the wavelength of light) is known as Rayleigh Scattering. This phenomenon was described by Lord Rayleigh, a renowned mathematician and Physicist and a Nobel laureate, hence the phenomenon is named after him.
Lord Rayleigh calculated that for a given angle of incidence, the scattered intensity of light is inversely proportional to the fourth power of wavelength. Sunlight is the full spectrum of light and consists of the entire visible spectrum.
Hence, during the daytime (for almost normal incidence), maximum scattering takes place for blue light (since it is at the lower end of the visible spectrum).
Another interesting phenomenon of the sky appearing red during the early and late hours of the day again depends on the angle of incidence which now becomes so large that the blue light is scattered at such a large angle that it does not reach the observer whereas the reddish-orange part of the visible spectrum is in the field of view of the observer.